MediaWorks announced on Friday that Barnett will leave his role at NewstalkZB in early 2025 and join More FM, where he previously worked for more than two decades.
Barnett currently co-hosts ZB's afternoon show with James Daniels.
He will co-host The More FM Breakfast Club with Lana Cochrane-Searle, Adam Percival and Paul Ego.
Cochrane-Searle said: “We are so happy to have our mate Si back on board with us!
“His infectious laugh and boyish charm will really brighten our mornings.
“We have so many fond memories of working with Si in the past and can't wait to create more magic with him soon.”
MediaWorks chief executive Wendy Palmer said she was pleased to welcome Barnett back to More FM.
“Simon is a hugely talented presenter who connects with Kiwis young and old,” Palmer said.
“He has such warmth, empathy and a real sense of fun. I know the team and our audience will love having him back on More FM.”
In January, Barnett returned to the airwaves following the death of his wife Jodi.
At the time, he told listeners that he always strived to be an “authentic broadcaster.” New Zealand herald reported.
“I will note that Jodi just enjoyed listening,” he said in January.
“I don't know if I will ever completely get over her loss, I don't want to either.
“The listeners have always been extremely good to me. Whether it's music radio or conversations, they've always been really nice to me.
“I really appreciated that kindness.”