He reached the ranks of lieutenant on 7 January 1947, captain on 27 September 1948 and served as executive officer at Armed Forces Training Headquarters.

He was armed forces commander in chief during the bloody crackdown on student protests surrounding the funeral of former UN Secretary-General U Thant.

He led both tactical and strategic campaigns against the Karen National Union as well as the Communist Party of Burma and various ethnic armed groups, especially in the north and east of the country.

According to the official explanation released by the then ruling party, the Burma Socialist Programme Party, he was forced to retire because Dr. Daw Tin Moe Wai, his wife, broke the rules and regulations laid down for the spouses of commanding officers of the Tatmadaw by accepting numerous bribes, thus affecting General Tin Oo's position.

He was subsequently arrested and tried for the alleged withholding of information concerning a failed coup-d'état against General Ne Win and the Council of State.

On 11 January 1977, Judge U Ohn Maung, Chairman of the Divisional Justice Committee for the Yangon Division sentenced him to 7 years of hard labour and imprisonment according to the Crime Against State and High Treasons Act 124.

On 30 May 2003, Tin Oo, travelling with the caravan of Aung San Suu Kyi, leader of the NLD, was attacked in the northern village of Depayin by a government-sponsored mob, murdering and wounding many of his supporters.

[1] Tin Oo was taken into detention along with Aung San Suu Kyi and was initially held in prison in Kalay in northwestern Myanmar.