The 30-year-old will link with former coach Kristian Woolf who was a Broncos assistant when he made his NRL debut in 2014. Woolf also coached Molo at the Townsville Blackhawks in 2018.
The move of the Samoan international and former Queensland prop comes after a tumultuous two months.
Molo had taken a leave of absence from Dragons training since early this year after taking umbrage with a comment from a coach.
AAP has been told part of Molo's exit includes a termination fee with the prop to pay back a sizeable sum to the Dragons, with whom he was signed until the end of 2026.
Molo's manager Wade Rushton said the move to the Dolphins was "not about money" and all about playing for a club where he had a strong relationship with the coaching staff and felt he could thrive as a man and footballer.
"There is a bit of paperwork between the two clubs going backwards and forwards but everyone is on the same page and Frank will be going to the Dolphins," Rushton told AAP.
"He will be going up there next week. There were a few Sydney clubs involved trying to get him but the Dolphins worked out as the best fit for him.
"Frank is most comfortable going there. He has played under Kristian Woolf before and knows (development coach) Kurt Richards and the crew out there.
"A lot of people have assumed it was a money issue but it wasn't. He is not going to the Dolphins for any more money than he was on at the Dragons.
"There was a hiccup at the Dragons with a staff member. It has been publicised what was said. We felt it was best making a move to a club that highly respected Frank on his line of not drinking any more and the Dolphins are a good fit for that."
Molo grew up in the Brisbane suburb of Zillmere, just 20km from the Dolphins' base in Redcliffe. He is a Norths St Josephs junior and familiar with the environs of his new home.
Molo has played 138 NRL games for the Broncos, Cowboys and Dragons and was a member of Wayne Bennett's 2020 Maroons outfit that won the series 2-1.Â
His arrival at the Dolphins will boost a pack that has lost founding captain Jesse Bromwich to retirement and that will be without Queensland prop Thomas Flelger until his long-term shoulder injury heals.
Molo's contract dispute had proven a constant headache for St George Illawarra as they were unable to sign a replacement given their top-30 roster was full.
They eventually released winger Mikaele Ravalawa to South Sydney for the rest of the season last week, allowing them to sign former Test prop David Klemmer.
But Molo's exit will clear significant salary-cap space, given he was on a deal in the vicinity of $550,000 per year for both 2025 and 2026.
The settlement means the vast majority of Molo's salary will not be counted in this year's cap, while his entire salary will be wiped from the 2026 cap.
There is also now one spot free on the Dragons' 2025 30-man roster.