Keith joined Finn Harps from Swilly Rovers in 2005 and made his senior debut for the club against Longford Town on 30 April. He remained at Harps for three seasons before returning to Swilly Rovers in 2008.

Keith spent two seasons back at Swilly Rovers before signing up for a second spell at Finn Harps in the summer of 2010. He made his return in a 3-1 away win over Mervue United on 7 August 2010 and made 8 league appearances over the latter half of the season. In 2011 Keith made 26 league appearances for Harps and scored his first league goal for the club against Longford Town in September. At the end of the season Keith was awarded Harps Player of the Year award.

Keith remained a defensive stalwart for Harps making 16 league appearances in 2012, 26 in 2013 and a further 23 in 2014. 2015 was a big season as Keith played in 22 First Division matches, scoring once in a 1-0 win over Athlone Town, before playing in all four play-off matches as Finn Harps were promoted to the Premier Division after overcoming UCD and Limerick. In 2016 Keith played in 27 of Harps' thirty-three Premier Division games as the Donegal retained their top tier spot with a tenth place league finish.

In January 2018, Keith re-signed for Finn Harps. Keith signed in December 2018 for another season ahead of the start of the 2019 campaign.

In January 2020, Keith signed for Glentoran where he played for eighteen months and won the 2020 Irish Cup. In June 2021 he moved on, signing for Dungannon Swifts, but his stay there lasted only until January 2022 when he came back to the League of Ireland and signed for Drogheda United.