Gilmore, 22, has scored one try in four appearances this season for Vikings, who are currently seventh in the Super League table.
"Tom is a really talented young man with a mature head on his shoulders," head coach Denis Betts said.
"I am excited for what the future holds for Tom."
Widnes scrum-half Tom Gilmore has signed a two-year contract extension to keep him at the club until the end of the 2018 season.