Career in Tonga
Wood was born in Geelong, the son of Alfred Wood (1867–1941) and Janet nee Wemyss (1866–1959), who were Salvation Army officers. He was educated in Sydney and initially qualified as a barrister in Victoria.
Converting to Methodism, Wood was ordained a Methodist minister in 1924 and left immediately to a missionary appointment in the Kingdom of Tonga, where he was Principal of Free Wesleyan boys' boarding school Tupou College. Under his leadership, the school moved from Nuku'alofa to Nafualu and grew from 30 students to almost 400, becoming the biggest school in the country. At Wood's instigation, scholarships were offered by the Tongan government to enable students to further their education in Australia, or go to Fiji for medical training. Wood learned the Tongan language fluently and wrote (English-language) books on Tongan history and geography which, in the 2000s, are still used as secondary school textbooks. Wood was also responsible for the training in Tonga of candidates for church ministry. In their 13 years in the Pacific nation, Haloti 'Uti (Harold Wood) and his wife, ' Olife (Olive), developed a special fondness and love for the people and the country. Early on, he supported Queen Salote with legal advice in her work to reconcile two Methodist factions and became well acquainted with and respected by the Royal Family and others.
Career in Melbourne
Returning to Australia in 1937, Wood became principal of Methodist Ladies' College (MLC) in Kew, Victoria, from 1939 until his retirement in 1966. From 1966 to 1977 he served as a parish minister at Deepdene Methodist (now Uniting) Church in Nungerner Street, Deepdene, Melbourne, which he caused to be renamed St Paul's.
Wood attained a doctorate of Divinity in 1947, with a dissertation on church union (published as Unity Without Uniformity ). He was President of the Methodist Church of Victoria and Tasmania in 1952–53 and President-General of the Methodist Church of Australasia 1957–60 (all while principal of MLC). An ardent advocate of church union, he lived to see the formation of the Uniting Church in Australia in 1977.
A renowned orator, Wood preached at least twice most Sundays and his sermons were frequently reported in the press. He was a regular at Speakers' Corner on the Yarra River, and a keynote speaker at the first National Christian Youth Convention, held in 1955. A vocal opponent of nuclear weapons, the Vietnam War and the White Australia policy, he was under ASIO surveillance from 1954 to 1972. Progressive in his day, he was never, however, a Communist.
Wood married North Shore medical doctor Olive K. O'Reilly in 1924.  They had six children, all born in Tonga. After Olive's death in 1976, he married Dora Walker (1920–2014). His daughter Elizabeth Olive Wood ( Elizabeth Wood-Ellem) was the author of a biography of Queen Salote of Tonga,  his youngest daughter, Monica Wood, better known by her stage-name Monica Maughan, was an actor for over 50 years, and his younger son, the Revd H. D'Arcy Wood, was President of the National Assembly of the Uniting Church from 1991 to 1994.
Wood died in Melbourne in 1989, aged 93.
The mainly Tongan congregation in Auburn, New South Wales named their church after him: Harold Wood Auburn Uniting Church.