The deal will see the Japan-based playmaker rejoin Canterbury for the 2026 National Provincial Championship and the Crusaders from the 2027 Super Rugby season.
"We're really pleased to have Richie re-committing to New Zealand Rugby," Chief Executive Mark Robinson said in a statement.
"He's a proven talent with a strong track record of performing on the biggest stages."
Mo'unga, capped 56 times for the All Blacks and a winner of seven championship trophies at the Crusaders, has been ineligible to play for New Zealand since leaving for Japan after the 2023 World Cup in France.
New Zealand Rugby restricts test selection to home-based players to try to protect its domestic competitions from talent drain.
His former coach at the Crusaders, Scott Robertson, is now the All Blacks coach and has been vocal about wanting Mo'unga home and pushing for selection.
Mo'unga helped Brave Lupus Tokyo seal back-to-back Japan Rugby League OnePhil titles in June while playing with a fractured hand.
"He has this gift of bringing out the best in those around him and we can’t wait to have him back in 2027," Crusaders CEO Colin Mansbridge said.
Mo'unga's return to New Zealand a year before the 2027 World Cup in Australia will be welcomed by home fans and give Robertson another option for the coveted number 10 jersey.
In Mo'unga's absence, Beauden Barrett has been Robertson's starting flyhalf in most recent tests, with Damien McKenzie the back-up playmaker.