Timlin signed for League Two club Stevenage on a free transfer on 11 June 2018. He made his Stevenage debut in the club's opening game of the 2018–19 season, playing the first 64 minutes in a 2–2 draw against Tranmere Rovers at Broadhall Way. Timlin scored his first goal for the club, which turned out to be his only goal for the club, in Stevenage's 1–0 victory over Morecambe on 18 August 2018. He played regularly throughout the season in the centre of midfield, making 46 appearances in all competitions.