Forward Walker was unable to stop the Robins suffering the heartbreak of relegation from Super League after their narrow defeat at the hands of Salford Red Devils in the Million Pound Game.
It has not taken the 25-year-old long to make a return to the top flight after putting pen to paper on a two-year deal at Langtree Park.
Saints boss Cunningham believes the Scotland international will fit in well at the club and is looking forward to having the player on board.
He was quoted by Sky Sports, saying: "Adam is a hard-working forward who will complement the dynamic pack we already have at the Saints.
"Along with his size, he has a big engine, good footwork and at 25 years old it's fair to say he hasn't hit his peak yet.
"We're looking forward to seeing him develop further at the club."