Loose forward Merrin, 30, made 28 appearances and was made captain in June.
However, the ex-New South Wales State of Origin star was given permission to seek a new club at the end of the season on “compassionate grounds.”
Leeds gave Merrin a deadline to secure an NRL club but Rhinos director of rugby Kevin Sinfield today confirmed he is heading back to Emerald Headingley.
“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,” said Sinfield.
“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.”