Trent Merrin reveals he'd been mulling over retirement since returning from the Super League

St George Illawarra Dragons forward Trent Merrin has revealed he'd been mulling over retirement ever since returning to the NRL from a stint in the Super League.

There's no longer a member of the Dragons' 2010 premiership-winning team in St George Illawarra's current squad after Merrin called time on his tremendous career today, effective immediately.

The decision brought to close a career stamped with 223 NRL games with the Dragons and Penrith Panthers, 13 appearances for NSW, six Tests with the Kangaroos and one season with Super League club the Leeds Rhinos in 2019.

Merrin's decision to retire from footy took the rugby league world by surprise, but the 31-year-old said it had "been on my mind" ever since returning from overseas after the 2019 Super League season.

"Since I got back from England it's always been on my mind - if I'm still up to it, if I'm still the same sort of person I am for the game," Merrin told 2GB's Wide World Sports radio host Mark Levy.

"I've been umming and ahhing for a while.

"I've been playing the game, seeing the changes to the game, obviously feeling the speed and the difference, (so) I thought it was time to let the young bucks take over."

The Dragons have surprised the league early in the 2021 season, bouncing back from their Charity Shield thumping at the hands of the South Sydney Rabbitohs to win four of their opening six games.

Among the best of coach Anthony Griffin's men have been young forwards Tyrell Fuimaono and Josh Kerr, two rising stars who'd even squeezed Merrin into starting on the bench in every one of the first five rounds.

Merrin said the club's blossoming crop of youngsters had helped him reach his retirement call.

"It's a monkey off the back, to be honest. It was one of the hardest things I had to do but one of the easiest things I had to do," Merrin said.

"As I said to the boys, the way that they're going, the way that the club is in good hands and the talent coming through - it made my decision a lot easier and ... it was a big relief. I took a big breath."