Bournemouth manager Eddie Howe has vowed to give his promotion heroes the chance to shine in the Premier League.
Wolves boss Kenny Jackett fears he will lose key winger Bakary Sako after his side missed out on a place in the play-offs.
The 27-year-old, who made seven appearances for the Hornets between 2010 and 2012, will provide competition for fellow keepers Heurelho Gomes and Jonathan Bond at Vicarage Road.
Gilmartin initially joined Watford from Walsall and has also had spells with Yeovil, Crawley and Plymouth.
He has spent the last year at Irish club St Patrick's Athletic.