Double champion Chadwick, who has won six races and finished on the podium in all except two of her 14 starts, joins Olympic champion Jenner's new outfit from Veloce Racing.
Chadwick beat Alice Powell to the 2021 title after a close-fought season-long battle, entering the final double-header at the Circuit of the Americas level on points.
The Williams Formula 1 development driver had previously said she had no plans to return to the series, telling Motorsport.com in November that she "didn't think it would make sense for me to return to W Series".
Following Tuesday's announcement, Chadwick said: "I am really excited to be returning to W Series to defend my title. To be asked to return by Jenner Racing was an opportunity I didn't think twice about.
"Together, we are focused on doing all we can to win title number three. I have spoken to Caitlyn Jenner and her vision for the team is amazing. I have zero doubt that she will be able to help take my career to the next level and open doors for me internationally.
"This is a big development year for me. I have plans to run a supporting racing programme and I have made no secret of my desire to compete in F3 and F2.
"But timing is everything and the opportunity that W Series gives me to get more competitive experience at world-class circuits is a key step on my journey towards competing in F1.
"I would like to thank W Series for their continued support, and I am looking forward to kicking off season three in Miami."
CEO Catherine Bond Muir said: "Jamie is an exceptional talent who has helped elevate the profile of W Series and inspire the next generation of female racing drivers with her performances on track – which have seen her become a two-time W Series champion – and off it where she has articulated our mission passionately and eloquently to a global audience.
"We are delighted that she has decided to defend her title, and I can't wait to watch her race at eight iconic circuits on the Formula 1 calendar for the Jenner Racing team."
W Series' 2022 calendar was confirmed in January, featuring its first ever Asian round and visiting five new venues.