The 22-year-old combative midfielder never really got much of a chance to impress at Glanford Park last season due to the team's good form and was released by manager Brian Laws this summer, after making one appearance in the LDV Vans defeat against Hereford.
"I'm a player that likes to win the ball, I'm very passionate about the game," said Barwick.
"I'm coming here and I want to play first team football. I am looking forward to it and I want to get Grimsby promoted.
"The season before last I was first in the pecking order. Then the manager decided to sign a couple of players and I never really got another chance. I just want to come here and prove myself."
Barwick made his debut for the Iron in the 2-1 defeat against Burnley in May 2000.
He made 47 starts for the club, scoring once in a 6-2 win over Huddersfield in November 2003.