Masayoshi Ōhira (大平 正芳, Ōhira Masayoshi, 12 March 1910 – 12 June 1980) was a Japanese politician who was Prime Minister of Japan from 1978 to 1980. Ōhira's time in office was cut short when he died in office; he remains the most recent Japanese Prime Minister to die in office (Keizō Obuchi was removed from office on 5 April 2000 after suddenly falling into a coma, a month before his death in May 2000).

He was born in present-day Kan'onji, Kagawa and attended Hitotsubashi University.

At the apex of his political life, Ōhira came to represent what were known as "mainstream factions" within the Liberal Democratic Party (LDP) which put him at odds with Prime Minister Takeo Fukuda, who led what were known as an "anti-mainstream" faction.^[1] Ōhira served as foreign minister in the cabinet of Kakuei Tanaka until mid-July 1974.^[2] In a cabinet reshuffle, he was replaced by Toshio Kimura as foreign minister.^[2] Ōhira was appointed by Tanaka as finance minister in the same reshuffle and replaced Takeo Fukuda in July 1974.^[2]

Ōhira was elected to the presidency of the LDP in late 1978. On 7 December 1978, he was appointed 68th Prime Minister, successfully pushing Takeo Fukuda from his position.^[3]

Ōhira was the sixth Christian to hold this office after Hara Takashi, Takahashi Korekiyo, Ichirō Hatoyama, Tetsu Katayama, and Shigeru Yoshida.

In the general election of 1979, the LDP narrowly failed to win an outright majority, but enough independent members of the Diet joined the party to enable Ōhira to remain in office, and he was duly reappointed on 9 November of that year. On 16 May 1980, a vote of no confidence was held in the Diet.

Ōhira expected the motion to fail, and was visibly shaken when it passed 243–187. 69 members of his own LDP, including Fukuda, abstained. Given the choice of resigning or calling new elections, Ōhira chose the latter and began campaigning for LDP candidates. He was hospitalized for exhaustion on 31 May and died of a massive heart attack 12 days later.

Chief Cabinet Secretary Masayoshi Ito acted in Ōhira's place as deputy after his death. Yoshio Sakurauchi, the Secretary General of LDP, led the LDP to its greatest victory in fifteen years, capitalizing on the "sympathy vote" generated by Ōhira's death. The Prime Minister was succeeded by Zenkō Suzuki after the election.

In 1979, Ōhira was the chairman and host of the 5th G7 summit in Tokyo but his fatal heart attack on 12 June happened only days before the 6th G7 summit was about to begin in Italy. Ōhira's colleague, Foreign Affairs Minister Saburo Okita, led the delegation which represented Japan in his place. Others joining Okita in traveling to the Venetian island of San Giorgio Maggiore were Finance Minister Noboru Takeshita and the head of the Ministry of International Trade and Industry.^[4]

Ōhira was a convert to Christianity during his time at the Takamatsu Higher School of Commerce (now the Takamatsu College of Economics), though without becoming a member of any formal Christian organization.^[5][6] However, others have stated that he was a member of the Anglican Church during the 1970s.^[7]