He must retain it in the September general election to keep his party alive, and there's speculation Mr Harawira has agreed not to field a candidate in Waiariki.
Mr Flavell retained the seat in 2014 but Mana's Annette Sykes put in a strong run.
In return, the Maori Party could stand aside in Te Tai Tokerau.
Mr Harawira lost the seat in 2014, narrowly beaten by Labour's Kelvin Davis, and the Mana Party ceased to have a presence in parliament.
The Maori Party's candidate drew more than 2500 votes, and it's likely most of them would have gone to Mr Harawira if he'd been given a clear run.
Since then both parties have acknowledged they can't afford to split the Maori vote, and it's possible the agreement could extend beyond Waiariki and Te Tai Tokerau.
Mr Morgan and Mr Harawira appear to have healed the bitter divisions between their parties.
Mr Harawira was a Maori Party MP until 2011 when he quit, accusing it of supporting government legislation which disadvantaged Maori.
He resigned from parliament, formed the Mana Party, fought a by-election in Te Tai Tokerau and won.
Several reconciliation attempts failed, and Mr Harawira continued as an MP until he lost the seat to Mr Davis.
- NZN