The team announced on Wednesday that reigning Super Formula champion Cassidy will join for 2021 after Bird announced on Tuesday that he will leave to join Jaguar for the new season.
Cassidy, a champion also in Japanese Super GT and Formula 3, will partner Robin Frijns as he competes in his first full Formula E season.
The Kiwi driver participated in the rookie test last March in Marrakesh with the team, setting a new lap record in the process and topping the times throughout the session.
“It’s a fantastic opportunity for me to be joining Formula E and Envision Virgin Racing from next season,” Cassidy said.
“The team is one of the most successful on the grid, have a great set-up and facilities, and have continually impressed me since I joined them for the Rookie Test back in March.
"All drivers know the depth and quality of the field in Formula E is among the best in the world, so it is great to be adding my name to this roster.”
“Racing in Japan has been an amazing experience and I’m fortunate that I’ve been able to achieve so much in a short space of time, but I feel it’s now time for the next challenge in my career and I’m very much looking forward to doing that with Envision Virgin Racing and Formula E.”
The team’s Managing Director Sylvain Filippi added: “As a team, it is always important to look ahead to ensure our long-term success. In Nick, we know we have a very ambitious, capable driver with raw talent, speed and racecraft, as well as an impressive track record for his age.
"Moving to become a world championship next season, we know Formula E is going to be as competitive as ever, but from his short time with us, we are confident – together with Robin Frijns – we have two drivers that can compete at the sharp end to win championships.”
Bahrain International Circuit - Winter testing