In his career, the Paraparaumu-born Coles made his debut in 2007 for Wellington and played 71 times for the province, out of his Poneke club. He made his debut for the Hurricanes in 2009 and played 141 times until retiring from Super Rugby in 2023.
He made his All Blacks debut in 2012, sharing in the World Cup triumph in 2015. He played three games for the Māori All Blacks in 2010 and rounded out his career earlier this year with 10 games for Kubota Spears.
Wellington coach Alando Soakai said he was thrilled Coles joined the group.
"I first reached out to Colesy and asked whether he was keen to play. He mentioned coaching, and the rest is history.
"We know he's got a lot of knowledge to pass onto the next generation of hookers, and we're lucky to have him. For him to offer some of his time to us is a testament to his incredible character, and his love for the Lions, the team that started it all."
Coles said, "Wellington has given me so much throughout my career, and for me to give back to the game, and the Union that started it all, is a no brainer.
"I've got some great memories with the Lions. My time in the black and yellow jersey is done, but I'm excited to direct my energy and efforts into coaching and, hopefully, given back to the next generation of players."