Barr made his inter county championship debut against Wicklow in 1989. Keith was on the 1995 All-Ireland winning team when Dublin narrowly defeated Tyrone. He won two National football league titles with Dublin, in 1991 and again in the National football league final replay against Donegal. Although, Keith had come on as a substitute against Donegal in 1993, he did not appear in the replayed game but still received his winners medal. Barr has been rewarded for his solid performance for Dublin with two GAA All-Star awards, the first in 1991 and the second in Dublin's All-Ireland winning year. He also has a Compromise rules medals for Ireland's victory over Australia in 1990.
In 1991, Dublin had a famous 3 draws in a row against Meath, a game which in Meath winning the fourth game by a scoreline of 2-10 to 0-15. It was claimed by Jimmy Keaveney, that Keith Barr's penalty miss was the turning point in the game. He was adamant that Barr had been instructed to take the point, but he went for glory and subsequently missed his chance. Although it is also claimed that the penalty miss was due to Mick Lyons of Meath running alongside Barr as he took the penalty, a penalty retake was never given.
The highlight of his career occurred recently when he joined the coaching staff at Gerldines GFC. Rumours around the Haggardstown club suggest he will be joining the club next year as player manager.