The Senegal striker, who already has 13 Premier League goals to his name this season, has signed a three-and-a-half year deal with the Champions League holders.
“When the club who won the Champions League wants you, the decision making is very easy,” Ba told Chelsea’s website.
“This club is massive and that’s something that helped the decision a lot. It was not a hard one.”
Ba’s Newcastle contract was believed to contain a £7m release clause and the Magpies accepted a bid from the Blues on Wednesday.
The 27-year-old added: “In two years now in the Premier League I have learned a lot and I keep learning.
“I just want to keep playing football and trying to score goals. I try to be strong mentally. This is a big part of the success of someone. If you are strong mentally then you have good chances to succeed.
“Yesterday I was looking back and smiling to myself, saying “Yes, I’ve done it.” I feel very proud, not only for me but the people who supported me over the years.”
Ba is available for selection for Chelsea’s FA Cup clash against Southampton on Saturday.
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