Tomkins, 21, initially joined the Red Devils on a one-month deal, but is now eligible to play against Widnes in the fifth round on Sunday, and also in the two games against his parent club later on this season.
Warriors Rugby Manager Kris Radlinski said: “We have agreed with Salford that Logan can now stay with the Red Devils for the rest of the season. Logan has enjoyed his initial month and is getting regular Football under Iestyn Harris, and after in depth discussions with the player it has been agreed that this agreement benefits Wigan, Salford and Logan.
“We have excellent cover here at Wigan with George Williams and Sam Powell who have impressed in recent performances in our First Team and the season loan also provides stability for him for the rest of the year. Logan will continue to be monitored by our staff and we are very confident that he will do a great job for Salford.”