The 32-year-old, who was FIFA's women's world player of the year in 2020, agreed a two-year contract with the west London club following her successful spell in Spain.
Bronze won seven trophies, including two Women's Champions League crowns, with Barcelona but ended her two-year stay when her contract expired in June.
The former Manchester City and Liverpool full-back returns to England, linking up with a Chelsea side who have won the past five WSL titles.
"To know I'm a Chelsea player still feels a little bit surreal," Bronze said.
"I'm really excited to be back in England. My family are so excited as well to get to more of my games.
"I'm excited to be in London, to see what the capital holds and to be at a club that is renowned for winning so many trophies."
Bronze has been capped 125 times by England and helped them to glory at the Women's European Championship in 2022.
She won the WSL title with Liverpool and City, while also enjoying multiple Women's Champions League triumphs during her time with Lyon.
