Justice Ayesha Malik, 55, had been selected by a commission that decides on the promotion of judges. As is typical for Supreme Court judges, she was sworn in on live TV, with her oath administered by Chief Justice Gulzar Ahmad.
"I congratulate Justice Ayesha Malik for becoming the first female judge of the Supreme Court," Prime Minister Imran Khan said in a tweet. "She has my prayers and good wishes."
The nine-member body that confirmed her appointment had initially turned down her elevation last year, before voting 5-4 to approve her this year.
Some lawyers' groups criticised the choice, arguing that she was picked despite not being among the top three most senior judges of the lower court from which she was elevated. They have called for objective criteria for the promotion of judges.