The west London side confirmed via a statement on their website on Wednesday morning that they had completed a deal to land Pulisic.
The USA international will now immediately be loaned back to Dortmund until the end of the season, with the 20-year-old set to link up with his new team-mates in the summer.
There had been plenty of speculation about Pulisic’s future in recent months, and the confirmation of the deal will please Chelsea FC fans.
Speaking in an interview quoted by Chelsea FC’s website, club director Granovskaia said: “We are delighted to have signed one of Europe’s most sought-after young players.
“Christian has shown his quality during a fantastic spell in Germany and at just 20, we believe he has the potential to become an important Chelsea player for many years to come.
“We look forward to welcoming him to Stamford Bridge in the summer and wish him and Dortmund every success for the remainder of the season.”
Meanwhile, the player himself said: “In the summer I move on to Chelsea and to a new competition, the English Premier League.
“It’s a privilege to have signed for such a legendary club and I look forward to working hard towards being a contributor to their team of world class players.”
It remains to be seen whether Chelsea FC will look to bring in any more players in the January transfer window.
The west London side are now focused on preparing for their FA Cup third round clash against Nottingham Forest on Saturday.
Chelsea FC are looking to try and finish in the top four this season under Maurizio Sarri.
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