The France international is in Paris, where he will undergo his medical before signing a three-year contract with the club.
Sources told ESPN that Matuidi has taken a pay cut to secure the move, and he will be reunited with Beckham, after the pair played together for Paris Saint-Germain back in 2013, just before the Englishman retired. Sources told ESPN that Matuidi has spoken to Beckham over the phone as well as with Inter Miami manager Diego Alonso.
He also spoke to Didier Deschamps, the France head coach, for whom he remains a key player in the 2018 World Cup winners' squad. Matuidi will be the 13th French player in MLS this season.
Matuidi has 84 caps for France and his signing represents a huge coup for Beckham's side, who recently called for patience after a difficult start for the franchise.
"Sometimes the road is long and [you] need to take a breather," Beckham wrote on Instagram. "Manchester United, Real Madrid, La Liga and the [Premier League] wasn't built in a day. Teams players and clubs need time to flourish but when they do all the hard times seem so distant.
"It's important to take time to reflect on what we have achieved so far. I'm proud of my team, our club and the amazing fans that we have. Patience is a virtue."
Inter Miami is still seeking its first win as a franchise and finished at the bottom of its MLS Is Back Tournament group.
Matuidi becomes the first player to leave Juve following the departure of manager Maurizio Sarri and the arrival of his replacement, Andrea Pirlo.