Merrin and partner Jessica are expecting their first child, with the Kangaroos star allowed to hold negotiations with sides on compassionate grounds.
NRL clubs St George Illawarra and Newcastle were in discussions with Merrin but failed to match the pay grade that was offered by the Super League outfit after signing a four-year marquee deal to join the club.
“During last season Trent had to return home to Australia for some personal family reasons and given those issues at the end of the season we gave him the opportunity to look to see if he could source a deal with a club closer to home,” Rhinos director of rugby Kevin Sinfield said.
“He had our full support in doing this, but we knew there was also a strong part of him that wanted to come back.
“I spoke with him this morning and he confirmed that he would be returning to the Rhinos and we are delighted about the news and he will be back for the start of pre-season at the beginning of November.
“His performances on the field were outstanding for us last season. He is looking forward to getting back and is raring to go again.”