"He's like another coach. We will be managing [his workload], but with his knowledge, his mana that he has within the group, the passion that he has for the Chiefs, it was a no-brainer to bring him in."
Donald, 35, said he was stoked to be returning.
"There is a great group of lads to work alongside and I hope I can play my part in supporting the team both on and off the field."
The man who struck the winning penalty in the 2011 Rugby World Cup final had been playing in Japan recently, after nine games with Counties Manukau in the 2017 Mitre 10 Cup.
He could add to his 104 games for the franchise, with Damian McKenzie and Jack Debreczeni the current first-five options in the squad, with Marty McKenzie set to miss the start of the season due to injury.
Rising star Shaun Stevenson was pleased to have an experienced teammate back in the fold.
"He's managed to get back on the payroll at New Zealand Rugby, I'm not too sure how," Stevenson joked to D'Arcy Waldegrave on Radio Sport.
"I thought his movie would have got him a bit more coin, but obviously not, so he's come back for another rodeo. It's good to see him back in the environment."
Stevenson said that Donald's knowledge will add plenty to what is a young Chiefs backline.
"He's as sharp as ever. Maybe he's lost a touch of pace and a bit of muscle, but he's a World Cup champion.
"I think the oldest player on our team was about 29, so he takes the average age up now since he's about 40. It's real good to have him back in the mix - our backline's pretty inexperienced, so he brings that leadership and that voice that we probably needed."
The Chiefs get their campaign under way against the Highlanders on Friday night at Waikato Stadium.
