The 2020-21 Formula E runner-up and a title contender with Venturi last season, Mortara remains with the Monaco-based squad through its rebranding, having been with the team throughout his five-year tenure in the championship.
Guenther moves across from the Nissan e.dams squad to partner Mortara, ensuring that Maserati has two race winners in the team for its first tilt at a single-seater racing category for over 60 years.
Mortara chalked up four victories last season for Venturi, but ultimately fell short in his endeavours to secure a title as difficult weekends in Monaco and London resulted in no points for the Geneva native.
In the meantime, Guenther only managed six points amid a troubled season at Nissan - as the Japanese marque was hamstrung by a recalcitrant powertrain - but ie s a three-time race winner in Formula E with the then-BMW backed Andretti squad.
"As a half-Italian it's a privilege and a pleasure to be welcome to be joining Maserati," said Mortara.
"I've had the pleasure to drive all three generations of Formula E car, and [the Gen3] is obviously an evolution of the Gen2 car.
"We're pushing EV technology development, I cannot wait actually to be racing with the Gen3 car in Mexico."
"I'm very proud and honoured to be part of the Maserati family," added Guenther.
"Formula E is very special, because we get to see all these amazing cities, and we race in the heart of really incredible cities, like, for instance, Sao Paolo, next year, like Cape Town.
"Those are new venues that I'm very much looking forward to. I think it's an exciting journey, and makes me very proud to compete in the future for Maserati.
"Edo and myself have both been winning races in the past, and Maserati is a big and famous brand. We will try to put the name where it belongs - at the very top.
"We will be pushing very hard with the new Gen3 car, which is obviously very exciting, very powerful, lots of new challenges. I really can't wait to get everything started."
Nyck de Vries had initially been in the frame for a Maserati drive in 2022-23, but his move into Formula 1 with AlphaTauri meant that the 2020-21 champion was no longer an option.
The announcement of Mortara and Guenther leaves just McLaren's second seat to be announced, and it has been indicated to Autosport that Jake Hughes will partner Rene Rast at the team.
