He joins the club after graduating from Gateshead's academy, and has recently spent time on loan at Newcastle Benfield in the Northern League last season.
Leech drew plaudits for his performances for the Lions, helping them to a 10th-placed finish in the league.
He made his senior debut for Gateshead against Alfreton Town in the National League North during the 2021/22 season.
He also captained their U19s team to two pieces of silverware, winning the National League U19 Alliance Division 1 as well as securing the League Cup.
Now, Leech joins the Seasiders following the expiration of his contract with the Tynesiders.
He becomes the club's fourth new signing of the summer, following in the footsteps of Nathan Dale, Dan Myer and Jake Hackett.
"I'm very pleased to get Lewis signed," Marske United Manager Graeme Lee said.
"I've had many good reports on Lewis, and after seeing him in training realised quickly we wanted him signed.
"He is a player who is hungry to do well. We are always looking to bring in young players who will move forward with the club and Lewis ticks all them boxes."
Photo credit: Gateshead