Danny East arrives at Blundell Park from Portsmouth, after his contract ran out at Fratton Park.
The 23-year-old never played first team football for the Tigers, but has played nearly 40 games in the Football League.
The versatile player, who can play anywhere across the defence or in midfield, originates from Hessle and he went onto make his Tigers full début in 2011.
East, is the Mariners boss Paul Hurst's first signing of what is expected to be a busy summer as they look to push for promotion back to the Football League once again.
Grimbsy hoping to bounce back after play-off heartache
Last season's regular right-back and last year's Player of the Year, Carl Magnay left for League Two side Hartlepool United.
The Mariners lost 5-3 on penalties to Bristol Rovers in last month's Conference play-off final.
The 23 year-old came up through the youth system at Hull City and also enjoyed loan spells at Gillingham and Northampton before signing for Pompey in the Summer of 2013.
East played 19 league games in a two-year stay at Pompey, scoring once – the winner at Northampton in April 2014.
The defender was loaned to the Mariners' Conference rivals – Aldershot – at the beginning of last term where he made six appearances.
East pleased to have returned 'home'
Speaking about the move East said: "I am very happy, to be back home and settled."
"The gaffer knows what he wants," admitted East, who added: "He's a great manager and knows what he wants.
He continued: "They've obviously been up there the last few years and I hope it comes off for him, the team and the fans.
An extremely versatile player, East spoke of his abilities: "I've played here a few times with Hull and I will always give my all but I think there is a lot to my game then that.
"I've got energy, I think I'm technically quite good - so I believe that I have a lot to give." said East.