The hard-working right-armer is closing in on 300 first-class wickets and has clocked 14 T20s and six ODIs for his country.
The 30-year-old joins Notts for their final two red-ball matches — the first of which is against Kent and got under way at 9.30 last night (NZ time).
Duffy, who picked up a New Zealand playing contract this season, played two Championship games for Kent in 2022 and claimed a five-wicket bag in the second innings of his county debut.
Notts will be hoping for something similar.
The East Midlands side are third from bottom with an 11-point buffer on Lancashire, who are in the second relegation spot.
"Jacob is an exciting signing at a crucial time in the season for us," Notts head coach Peter Moores told the club’s website.
"He’s got experience under his belt, and his skill set and time spent in England previously means he has the ability to make a difference in our remaining two games."
Duffy replaces South Africa Dane Paterson, who has returned home to the Republic following the birth of his second child.
Notts’ final game of the campaign is against Warwickshire and begins on September 26.
Duffy will return to Dunedin following that match to begin preparations for the New Zealand domestic season. Otago have a training camp planned for Alexandra in early October.
The domestic schedule has not been released yet, but it is understood the season will get under way with a flurry of one-day games in late October.
