The 27-year-old Senegal international was a surprise hit in the Premier League last season, scoring 16 league goals for Newcastle after joining the club on a free transfer from West Ham United.
His form has continued this campaign. Ba has scored 13 goals in 20 Premier League appearances—enough to convince Chelsea to trigger the release clause in his contract and pay a reported £7 million for his services.
The deal was made official on Friday. Said Ba, as per Chelsea's official website:
It feels good to be here, I'm very happy and very proud. It was important for me, and for Newcastle, to get my future sorted and now we can move on. Now they have the whole month to buy someone and for me as well, the sooner the better. Now I am here I just need to get settled in.
When the club who won the Champions League wants you, the decision is very easy. This club is massive and that's something that helped the decision a lot. It was not a hard one.
Ba is available to play for Chelsea in their FA Cup tie against Southampton this weekend. As Chelsea's official statement points out, however, he will be ineligible for their Europa League campaign—having played for Newcastle in the same competition this season.