Kante, whose Chelsea deal officially expires June 30, will join Karim Benzema at the Jeddah-based club and becomes the latest big name to move to Saudi Arabia following Cristiano Ronaldo's transfer to Al Nassr in January.
"The contract [with Kante] was finalized on Tuesday, June 20th, after he completed his medical tests at a specialized medical center in Dubai", Al-Ittihad said in a statement. "This move comes as Ittihad, who recently won the Saudi Professional League, aims to strengthen their squad.
"Kante's addition to Al-Ittihad is considered one of the most high-profile and impactful signings in the club's history. It is part of the club's efforts to establish itself as a top choice for world-class players in the Saudi Professional League."
The 32-year-old's deal will see him paid around €86 million ($109.78 million) per year, according to reports.
ESPN reported in February that Kante was close to signing a new contract with Chelsea, but no deal was finalised and the midfielder has now decided to end his seven-year stay at Stamford Bridge.
After playing a key role in Leicester City's shock Premier League title win in 2016, Kante moved to west London, where he became the first player since Eric Cantona in 1993 to win back-to-back English top-flight titles with two different teams.
Further success followed when lifting the FA Cup in 2018 and winning the Europa League the following year before landing the Champions League crown in 2021. But injuries limited him to just nine appearances in all competitions during a turbulent last season for Chelsea.
Despite spending more than £600m on new signings since Todd Boehly and Clearlake Capital took over the club last May, Chelsea finished a lowly 12th in the Premier League. Thomas Tuchel and replacement Graham Potter were both dismissed as managers during the campaign before the season ended with Frank Lampard in interim charge.
Following the appointment of Mauricio Pochettino as manager last month, it is set to be another summer of upheaval at Chelsea with several players -- including Christian Pulisic, Mateo Kovacic and Mason Mount -- looking likely to depart.