[7] Gilmartin did not feature for Walsall over the next two seasons, but played for Republic of Ireland under-21s in 2007, and completed his UEFA B coaching licence in April 2008.

[15][16] He made his debut in a League Cup first round tie away to Aldershot Town, keeping a clean sheet in a 3–0 Watford win.

Gilmartin struggled to displace Scott Loach as Watford's goalkeeper during the 2010–11 season, but did play in all four of the club's cup games.

[19] In February 2012 he joined League Two side Crawley Town on loan as back up to Michael Kuipers, following an injury to Scott Shearer.

[21] Gilmartin signed a two-year contract with League Two side Plymouth Argyle in July 2012,[22] and made 16 appearances in all competitions.

[25] Gilmartin returned to Dublin in July, having signed an 18-month contract with League of Ireland side St Patrick's Athletic.

[26][27] He made his Pats' debut later that month in a Dublin derby at Shamrock Rovers in the League of Ireland Cup.

[28] He made his league debut the following season, on 2 June 2014 against Drogheda United, when he came on as a half-time substitute for the injured Brendan Clarke.

Gilmartin returned to English football by re-signing with Watford on a one-year deal on 25 August 2014 as a back-up to Heurelho Gomes and Jonathan Bond, two years after he first left the club.

[33] Gilmartin rejected the offer of a new contract in July 2019 and signed for Championship club Bristol City as a player with some Junior Coaching responsibilities.