A familiar face at Blundell Park, Cartwright previously spent the 2023/24 campaign on loan with Grimsby, making 32 appearances and winning the club's Young Player of the Year award.
The Grimsby-born stopper actually began his career in the town's own academy before moving to Hull City's youth setup in 2015, and has since gathered further senior experience through loan spells at Peterborough United, Wycombe Wanderers and, most recently, Hartlepool United, where he made 13 appearances and kept seven clean sheets before a knee injury cut his campaign short.
Grimsby had to fend off interest from League Two rivals Crawley Town to get the deal done, with reporter Alan Nixon having first revealed that both clubs were tracking the 24-year-old this summer as Hull weighed up his prospects following their own promotion to the Premier League.
Cartwright now returns to reunite with goalkeeping coach Steve Croudson and link up with David Artell's squad, who reached the League Two play-offs last season before being knocked out by Salford City at the semi-final stage. Speaking after completing his return, Cartwright said: "I'm absolutely delighted to be back here; it means a lot more to me being a Town fan growing up.
"I remember coming to Blundell Park as a young lad and dreaming of playing in goal, so this is really special."
With Hull now preparing for life in the Premier League, regular football looked unlikely for Cartwright at the MKM Stadium, where he has made only three senior appearances across his career to date despite being under contract until 2027. Hull's goalkeeping department has been reshaped this summer with the arrival of Jack Butland, while Dillon Phillips and Thimothée Lo-Tutala provide further competition, leaving little room for Cartwright to force his way into first-team contention.
The loan gives both club and player a clear path: Grimsby gain an experienced, well-liked figure between the posts for their promotion push under Artell, while Cartwright gets the regular first-team football his development now requires as he looks to rebuild momentum after a season disrupted by injury at Hartlepool.