George Colley was born in Dublin an 1925. He was the son of Harry Colley, a TD and former adjutant if the IRA. He was educated at Marino CBS in Dublin. His life-long rival, Charles Haughey, was a classmate at CBS. He studied at University College Dublin and qualified as a solicitor.
In 1961 Colley was elected TD for Dublin North-East. Under Sean Lemass he held a number of posts, including Parliamentary Secretary to the Minister for Lands (1964); Minister for Education (1965; Minister for Industry and Commerce (1966).
In 1966 when Sean Lemass announced his retirement Colley and Haughey became the first two candidates in the leadership contest. However, when Jack Lynch announced his intention to contest the leadership Haughey withdrew. When put to a vote Jack Lynch beat George Colley by fifty-two votes to nineteen. Under the new Taoiseach Colley remained as Minister for Industry and Commerce. In 1969 he was made Minister for the Gaeltacht while retaining his Industry and Commerce portfolio. Between 1970 and 1973 Colley served as Minister for Finance. He oversaw the transition to decimalisation of the currency in 1971.
In 1977 Fianna Fáil returned to power and Colley became Minister for Finance and the Public Service. In 1979 when Jack Lynch retired Colley competed for the leadership again. His rival was once again Charles Haughey. Haughey became Taoiseach and Fianna Fáil leader by a margin of six votes. Colley demanded a veto on Haughey's appointments to the Departments of Justice and Defence. This was granted. Following the 1982 general election he demanded the same, however this time his request was refused. Haughey refused to appoint Colley as Tánaiste. He then declined the offer of a minesterial post and retired to the backbenches.