The 26 -year-old qualifies for Australia as he was born in Melbourne and is set to play in the June test series against Six Nations champions Ireland.
The loose forward had two stints in Sydney club rugby with Randwick and has earned almost 30 caps for the Crusaders since making his debut in 2016.
Samu switched to New Zealand's Tasman and was spotted by the Crusaders and was Player of the Year in 2015 in their development team, the Knights.
He was called into their senior Super Rugby squad as injury cover at the tail- end of that campaign and earned a Crusaders contract for 2016.
Samu has started five games this season and also made four appearances off the bench.
"I'd like to thank the Crusaders for giving me a chance at this level and wish them all the best for the future." Samu said.
"I am thrilled by the challenge of joining the Brumbies and am looking forward to taking to the field for the club."
Samu is renowned for his hard running and tough tackling.
"Peter is a powerful backrower with good speed and a skill-set that suits how we want to play at the Brumbies," said Brumbies' head coach Dan McKellar.
"He comes from a highly successful program and has enjoyed success at both Mitre 10 Cup and Super Rugby level."