Sexton was born in Dublin, but has family ties to North Kerry; he is a nephew of former Garryowen, Munster and Ireland rugby player William Sexton. He attended St Mary's College, Dublin and scored a drop goal in the dying moments of the school's 2002 Leinster Senior Cup final win. His performances at St. Mary's led to Sexton being selected for Leinster. He made his debut against Border Reivers in 2006.
Sexton was part of Leinster's Celtic League winning side in 2007–08. On 2 May 2009 he established himself in the Leinster first team, replacing the injured Argentine fly-half Felipe Contepomi as an early substitute in the Heineken Cup semi-final to help Leinster beat rivals Munster a convincing 25–6. He then started in Leinster's home match against the Scarlets in the Celtic League, scoring 15 points (including a try) in a man of the match performance.
Contepomi's cruciate ligament injury ruled him out for the rest of Leinster's campaign; he signed for French giants [Stade Francais] the following season. Sexton started the 2009 Heineken Cup Final against Leicester Tigers, and kicked a spectacular drop goal from the halfway line and also kicked the winning penalty (a total of 11 points, 2 penalties, 1 drop goal and 1 conversion). Leinster went on to win their first European Cup 16–19 at Murrayfield.
Upon recovering from a hand injury sustained during the Ireland South Africa autumn international fixture in 2009, Sexton helped Leinster to secure a bonus point win over Brive in the Heineken Cup to take command of their pool. The following week in their pool decider, Sexton scored a drop goal in the dying minutes against London Irish at Twickenham to even up the score at eleven all. This secured Leinster a home advantage in the Heineken Cup quarter finals and knocked the Exiles out of the competition. Sexton's ability was highlighted on his return from injury in the 2010/11 season, where he helped Leinster recover from a shaky start to the season as a second-half substitute in their win over Munster in the Celtic League. Following this victory, he helped Leinster win over Racing Metro and Saracens in the Heineken Cup. In the second match, he received a man of the match award after scoring 25 points, including a try, giving his team the top spot in a pool regarded as one of the most competitive in Heineken Cup history. A poll taken by planetrugby.com following these performances suggested that Sexton was currently regarded as the top fly-half in Europe.
Sexton played three games in the 2006–07 season. Although he only played 12 minutes against Ospreys, he scored a conversion. He went on to kick three penalties in his other games, which were against Ulster Rugby and Munster Rugby. In all, that season he scored 11 points in only 143 minutes play.
In the 2007–08 season, Sexton started against Edinburgh Rugby and scored one try, one conversion and two penalties. He scored his second try of the season against Cardiff Blues, in which game he scored a further two conversions and two penalties. He followed that up by scoring a conversion and two penalties against the Scarlets. He ended 2007 scoring a further 23 points against Ulster Rugby and Glasgow Warriors. He then finished off the season with 14 points in his games against Munster Rugby and Newport Gwent Dragons. Overall, he scored 73 points during 2007–08.
At the start of the season, Sexton played seven matches against Cardiff Blues, Edinburgh Rugby and Munster Rugby in September. In October, he played against Connacht Rugby, Edinburgh Rugby, London Wasps and Glasgow Warriors. He finished the season on a high, scoring 64 points after November. He got a call up to the Ireland team for the 2008 Six Nations but was ruled out by injury.
Sexton played against Scarlets, Dragons, Ospreys, Edinburgh, Munster, London Irish, Brive, Ulster and Cardiff before being called up to the Ireland team for a match against Fiji. He scored five conversions and two penalties in that match. He then played against South Africa, scoring five penalties. In 2010, Sexton played six games for Ireland, scoring 37 points in matches against England, Wales, Scotland, New Zealand and Australia.
Sexton played 19 times for Leinster that season, scoring 237 points. He scored two tries as Leinster won the Heineken Cup after trailing 22–6 at half time to win the match 33–22. Leinster then had the chance to add a second trophy by winning the Pro12. However, Munster beat them 19–9 in the final, with Sexton kicking three penalties.
During Leinster's 2011 Heineken Cup final against the Northampton Saints, Sexton scored 28 points including 2 tries in a historic comeback, when Leinster beat Northampton 33–22 at the Millennium Stadium after falling 22–6 down at halftime. Sexton won the man of the match award and his second Heineken Cup medal. His 28 points in that match makes him the second-highest scorer in one game in Heineken Cup history. Sexton stated that his career-defining performance was dedicated to his late grandfather, John Sexton – the hugely popular Listowel businessman who had died a few months earlier. However, Sexton and Leinster could not snatch the first Heineken Cup and Celtic League double that season, with the club losing to Munster in the 2011 Celtic League Final.
Sexton played 16 games for Leinster in 2011–12, scoring a try, 29 conversions, 3 drop goals and 4 penalties. He totalled 213 points overall. He won the Heineken cup with Leinster that year and came runners up in the RaboDirect pro 12, losing to Ospreys in the final. He started in all five matches in the six nations.
In May 2012, Irish heavyweights Leinster and Sexton achieved their third Heineken Cup triumph in four seasons against Irish rivals Ulster as they established themselves as true giants of the European game. First-half tries by flanker Sean O'Brien and prop Cian Healy put Leinster on the way towards a record-breaking triumph. Leinster's reign as Heineken Cup holders was never seriously threatened in front of almost 82,000 spectators at Twickenham. Jonathan Sexton kicked three conversions and three penalties for a 15-point haul as Leinster became the first team since Leicester Tigers in 2002 to successfully defend the Heineken Cup. When replacement prop Heinke van der Merwe and Sean Cronin scored near full-time, it gave Leinster the biggest ever winning margin in a Heineken Cup final, Leinster 42–14 Ulster.
The 2012–13 season proved successful for Sexton as he helped Leinster win their first Pro 12 title since the Celtic league, having been runners up the previous three seasons. Despite the disappointment of failing to gain access to the knockout stages of the Heineken cup that year, Sexton helped Leinster win their first Amlin Challenge Cup, a third European title in three years. He spent a portion of the season sidelined due to injury, allowing his understudy Ian Madigan to take the hot seat at outside half.
It was announced that Sexton would leave Leinster at the end of the season to join Racing Metro, as he had failed to agree terms with the IRFU, despite his outspoken intent to remain in the blue jersey for the remainder of his career. In January 2013, Sexton informed the IRFU that he would not be renewing his contract with Leinster. He left the province at the end of the 2012/13 season.
Racing 92 (2013–2015)
Rumours began to circulate midway through the 2012–13 season that Sexton had agreed to join Racing 92 in Paris at the end of the season for a salary reported in the region of 750,000 euros per annum (which would make him one of the highest-paid players in Europe). The reports were then confirmed by Sexton and Racing Metro after talks with the IRFU over a new contract had broken down. Sexton joined fellow British & Irish Lions teammates Jamie Roberts and Dan Lydiate as the club's marquee signings for the 2013–14 season, while his former adversary for the Irish 10 jersey Ronan O'Gara was confirmed as a coach for the club. Sexton stated that he had been unaware of O'Gara's arrival, but was happy at the news as both men had developed a good working friendship in their later years together in the Ireland set-up, despite a reportedly fractious early relationship during Sexton's emergence.
Sexton's departure came as a surprise to many in Ireland, as he had been a key player for both Leinster and Ireland in the preceding years, and had stated his intention to remain at the club. He cited the Parisian club's ambitious new project and impressive training facilities as factors in choosing them over traditionally more successful European clubs outside Ireland.
In Sexton's first year as a non-Leinster player, Racing Metro struggled to impose itself as a force in Europe, as they failed to qualify from the group stages of the Heineken Cup.
Return to Leinster
Following speculation during the summer of 2014, Sexton announced in September 2014 that he had signed a contract to bring him back to Leinster for the 2015–16 season until at least November 2019.
Sexton was selected to play for Ireland A in the 2009 Churchill Cup. Ireland A went on to win the tournament, beating England Saxons 49–22 in the final with Sexton scoring 15 points despite being sin-binned.
Sexton won his first cap for Ireland in the Test against Fiji at the RDS in Dublin on 21 November 2009 scoring 16 points (5 conversions and 2 penalty goals), kicking 7 from 7 in extremely difficult weather conditions and winning Man of the Match with his impressive International debut.
On 24 November 2009, Sexton was selected ahead of veteran fly-half Ronan O'Gara in Ireland's autumn international against world cup champions South Africa at Croke Park. He kicked all of Ireland's 15 points and, after the match, it was revealed that Sexton had played out Ireland's thrilling 15–10 victory with a broken hand.
Sexton returned to the Ireland squad for the 2010 Six Nations, he came on as a substitute in Ireland's loss against France. He was selected to earn his first Six Nations start in the match against England in Twickenham on 27 February 2010. Ireland won the game 20–16 at Twickenham with Sexton before being replaced by Ronan O'Gara late in the game. Sexton started against Wales and Scotland, being replaced by Ronan O'Gara in both games towards the end. Over the six nations, his kicking success rate was much lower than in his first few tests, missing several kicks.
Sexton was named in Ireland's squad for the 2010 Summer Tests, coming off the bench to replace O'Gara against New Zealand. He started against New Zealand Maori and kicked 23 points, and started against Australia, kicking all of Ireland's 15 points in the game.
Sexton then went to international duty and played in matches against South Africa, New Zealand and Argentina. He scored 34 points in those tests, but then he had to prepare for the 2011 Six Nations Championship. He played the first game in the win against Italy being replaced by Ronan O'Gara, who scored the winning drop goal. He then started in the 22–25 defeat against France but Sexton was then dropped to the bench against Scotland because of O'Gara's leading form. ,He then was dropped to the bench against Wales. Against England though Sexton was started and kicked 14 of the points in a famous 24–9 win. Sexton was named RBS 6 Nations Man of the Match following his role in Ireland's successful attempt to stop England's hunt for a Grand Slam in the 2011 RBS 6 Nations.
Sexton also played for Ireland in the 2011 Rugby World Cup.
Sexton was arguably Ireland's most influential player in their 2014 Six Nations win and was the joint highest try scorer in the championship with four tries. In the final match against France in Paris he scored two tries and scored 17 of the teams 22 points on their way to winning the match and with it the 2014 RBS 6 Nations Championship. The match was also notable as being Brian O'Driscoll's last ever game in an Ireland jersey. Despite worries of a thumb injury hindering his participation midway through the competition, Sexton competed in every game, losing only one to England at Twickenham.
As a result of his performances for club and country, Sexton was selected to play for the 2013 British and Irish Lions in their tour to Australia. He played in all three of the tests, scoring one try.
Sexton was then selected for the 2017 Lions tour of New Zealand. Sexton came off the bench for the first test against New Zealand and started in the second and third, despite being seriously injured with a broken wrist and ruptured ankle before the third test. Sexton played the majority of the third test before being replaced by Ben Te'o.
British & Irish Lions
2017 British and Irish Lions tour to New Zealand
Sexton has been a key figure to Irish and club rugby due to both his defensive play and his good passing in attack. He is also a place-kicker for both club and country. As of June 2013, Sexton has scored 282 points in all test matches, including 115 points in four seasons in the Six Nations Tournament. As of the 7th of October 2017, Sexton became Leinster's all-time leading points scorer (overtaking Felipe Contepomi in the process) with 1234 points.
In May 2012 former Ireland and Leinster fly-half Ollie Campbell stated before Leinster's third European Cup in four years that Sexton is a "class act with hardly any weaknesses", and that during Leinster's rise to the summit of European rugby the "only significant Heineken Cup defeat over the last four seasons occurred when Jonathan Sexton was not playing".