The Frenchman expressed his joy over the news.
"I am delighted to continue my journey and adventure at Chelsea," Giroud said in a statement. "I can't wait to get back to playing and enjoying competitive football with my team-mates.
"I'm looking forward to wearing the Chelsea shirt again, especially in front of our fans at a full Stamford Bridge, whenever it is safe to do so."
Giroud had been linked with an exit from Stamford Bridge, with Inter close to signing him in January.