Jarvis was not retained by the Meyer Shank Racing Acura team after he clinched the final crown of IMSA's DPi era with Tom Blomqvist, having signed up for an LMP2 programme with United in the WEC that took precedence.
The 2005 McLaren Autosport BRDC Award winner and former Audi LMP1 racer will be reunited with Blomqvist for select rounds of the 2023 WEC - with ex-Formula 1 racer Giedo van der Garde joining the team when the Anglo-Swede is unavailable - and continue with regular 2022 co-driver Josh Pierson.
But Jarvis will also contest the ELMS for United alongside team regular Phil Hanson, the 2020 series champion, and F2 convert Sato.
The Japanese managed a best finish of eighth in his three seasons of F2 with the Trident and Virtuosi squads.
Jarvis's signing follows the recent announcements of several high-profile WEC drivers into the European series' LMP2 class, with Peugeot Hypercar driver Paul di Resta also committing to United in a lineup that features 2003 Le Mans 24 Hours winner Guy Smith, while Toyota's Jose Maria Lopez and former Porsche driver Neel Jani have signed with Cool Racing and Duqueine respectively.
Porsche driver Gianmaria Bruni will also continue with Proton after winning the Daytona 24 Hours in LMP2 last weekend, while two-time ELMS champion Louis Deletraz will also defend his title after switching from Prema to the TF Sport-run Racing Team Turkey operation.
"I know Phil extremely well and look forward to working with Marino for the first time having watched him in F2," said Jarvis, who added victory in the Daytona 24 Hours last year to his 2013 win in the Sebring 12 Hours.
"It will be my first full season in the championship but being part of a proven race-winning team, with extremely strong team-mates, I’m confident we can challenge for victories."
"I would like to thank everyone in the team for their trust and everyone around me for making this happen," added Sato, who also drove for the AlphaTauri Formula 1 team in the 2020 young driver test in Abu Dhabi.
"It will be a new challenge for me but I’m sure we can have a great season – I’m excited to get started."
Team co-owner Richard Dean said: "This is a super strong driver line-up. We’ve strengthened our team in so many areas as we have our sights solely focussed on winning back our European Le Mans Series title."
