Nonu, who played for the Blues last season after spending nine years with the Hurricanes, will join up with the Dunedin-based side early next year if contract negotiations are completed successfully.
Highlanders head coach Jamie Joseph said signing the 30-year-old would be a massive boost for the team.
"Ma'a has been a standout performer for the All Blacks over his playing career and he would bring some great playing form to our squad next season," Joseph told the Highlanders' official website.
"He has a lot of big match experience at international level and we know that we would benefit from that."
Nonu, who made his All Blacks debut in 2003 against England, signed with the Blues after being sensationally dumped by the Hurricanes in 2011.
General manager Roger Clark said Nonu's decision to open talks with the Highlanders was a reflection of the team's progress.
"Ma'a is a world-class player who would add real excitement to the Highlanders in 2013," he added. "It's testament to the work the coaching and management team have put in both on and off the field that a player like Ma'a has decided he'd like to join us."
The Highlanders are scheduled to kick off their 2013 Super Rugby season against the Chiefs on February 22.
- Jamie Joseph