Barnes joined Conference North club Gainsborough Trinity on a non-contract terms in April 2009 after the club needed an emergency goalkeeper to cover for the injured Adam Sollitt, making his debut in the final game of the 2008–09 season, a 3–2 victory over Harrogate Town. Trinity manager Steve Charles praised Barnes as he was given Man of the Match in the game, but commented signing Barnes for the 2009–10 season was unlikely due to the players desire to play at a professional level. Despite this though, Barnes signed a permanent contract for the club on 9 June 2009 as well as the club signing Darryn Stamp on the same day. Barnes was joined at Trinity by a vast number of professionals as new chairman Peter Swann boosted the club's finances to sign a higher calibre of players. Barnes would start the 2009–10 season off as the club's number 1 keeper. The Holy Blues appointed Brian Little as manager who in turn brought in former Premiership keeper Gavin Ward as his Assistant Manager and second choice keeper.