The 33-year-old has signed a two-year contract at Stamford Bridge, with the option of a further season, and arrives for a £12m fee while Marcos Alonso will join Barcelona.
It comes less than nine months after Aubameyang left the Premier League after having his contract terminated at Arsenal.
“I’m really happy, it’s an honour to be part of this team and I can’t wait to start,” Aubameyang said.
Chelsea sign Aubameyang
“I have some unfinished business with the Premier League so it’s good to be back and really exciting.”
Chelsea have had a record-breaking transfer window, with the Aubameyang move taking their spending to £273.5million for the summer.
Todd Boehly has made an immediate impact as chairman, recruiting aggressively to try and help address the problems Chelsea have on the pitch.
“Pierre-Emerick is an elite striker with a proven track record in the Premier League and his arrival strengthens our squad, giving us new attacking options,” Boehly said.
“We are thrilled to have Pierre-Emerick on board with us in the new era at Chelsea and we’re really looking forward to working with him.”
Denis Zakaria also completed a move to the Blues, on a season-long loan deal. It’s understand Chelsea will have the option to make it a permanent move next summer for £26million.