As part of the deal, the New Zealand allrounder will also be available for the club's County Championship match against Warwickshire in late June
Northamptonshire have signed Jimmy Neesham for the 2022 T20 Blast.
The New Zealander represented Essex in last year's tournament and has played almost 200 times in the game's shortest format.
The Wantage Road county have regularly sought overseas allrounders in recent years, with Mohammad Nabi turning out in last year's competition and Kieron Pollard agreeing a deal in 2020, only for the Covid outbreak to prevent his arrival.
As well as Essex, Neesham has previously played for Kent and Derbyshire in county cricket, while he was a teammate of Northamptonshire stalwarts Josh Cobb and Graeme White in The Hundred at Welsh Fire.
"The club has a fantastic history in the Blast, and I hope that we can recreate those successes from 2013 and 2016," said Neesham, whose late cameo against England in the semi-final of last year's T20 World Cup played a pivotal part in taking his country to the final, where they lost to Australia.
Neesham played a key cameo in the T20 World Cup semi-final (Isuru Sameera Peiris/Gallo Images/Getty Images)
Referencing their time together in The Hundred, Cobb added: "He's a three-dimensional cricketer with genuine power and a high strike-rate in the middle order, but it was his character that stood out to me. He's someone who wants to win and is very selfless, he's a real team-first kind of player."
"I'm looking forward to having him here as a leader, to pass on his experience and help drive us to be better."
Neesham, who is set to be available for the entirety of the Blast, is the second New Zealand international to agree a contract with the county since John Sadler replaced David Ripley as head coach, with Test opener Will Young signing up as an overseas player for the LV=Insurance County Championship and Royal London Cup.
The terms of Neesham's deal are set to allow him to feature in the County Championship match between Northamptonshire and reigning champions Warwickshire.