Discussions between New Zealand Rugby (NZR) and the Welsh region mean an agreement has been reached over a compensation package that allows Mooar to be released early from his Scarlets contract.
As part of the agreement, Scarlets and NZR will explore high-performance partnership opportunities with each other in the coming years.
Mooar will look after the All Blacks attack when he links up with Foster and the rest of his new assistants.
Their first game will be against Wales later in 2020.
“To be joining the All Blacks coaching staff next year is an incredibly humbling and proud moment for my family and me,” Mooar said.
“The opportunity to help coach your country comes around very rarely so I would like to thank the Scarlets for allowing me to join the All Blacks.
“Similarly, I’d like to thank Ian and NZR not only for this opportunity, but also to finish this season with the Scarlets. The support I have had from both sides of the world has been amazing. The Scarlets players, staff, fans and board have all been superb and it is hugely appreciated by my family and me. I will continue to give it my all with this special group of people at the Scarlets this season to help us achieve our goals before we head back to New Zealand to join Fozzie and the All Blacks.”
Scarlets general manager of rugby Jon Daniels said: “Obviously, when we recruited Brad we both had a long-term plan for the region. Brad’s stay here will be brief, but he and the rest of the coaching staff have set us on a path and the next head coach will help us continue on that journey.
“We recognise that being part of the All Blacks coaching team is a huge opportunity for him. Our discussions with New Zealand Rugby have been extremely positive and we are grateful for their co-operation during the talks we have had.
“In terms of replacing Brad, we have already had a number of high-quality candidates express an interest in the role and as we have done in the past, we will conduct a thorough process to ensure we recruit the right man for the job once again.
“As for the immediate future, Brad is determined to build on the start we have had this season and we are all fully focused on a challenge for silverware in both the Guinness PRO14 and the European Challenge Cup.”
NZR head of professional rugby Chris Lendrum said: “We’re pleased to announce we have reached an agreement with Scarlets which will see Brad return to New Zealand in June at the conclusion of the club’s European competitions.
“We’d like to thank Scarlets for the positive, constructive and efficient approach they have taken around these discussions. We recognise the difficult position it put the club in, but they, like us, also recognised that it was a fantastic opportunity for Brad – the chance to coach his country.”
Lendrum said while details of the agreement between NZR and Scarlets were confidential, it did include the payment of some compensation for the Scarlets. There is also an intention to continue to foster links between the two organisations in the future.
All Blacks head coach Foster said: “We’re delighted to have Brad confirmed to join us. I know the new coaching group is excited and keen to get into their work next season and we’ll look forward to welcoming Brad in following his commitments with Scarlets. On behalf of the All Blacks, I’d also like to thank Scarlets for their understanding around Brad’s release. It is very much appreciated.”