The 32-year-old injured her anterior cruciate ligament in January 2024 and had to sit out the Paris Olympics as well as Chelsea's title-winning campaign last season.
Australia's all-time leading scorer showed she was keen to make up for lost time, her 100th goal for Chelsea helping the side to a 3-1 victory over hosts Aston Villa in the Women's Super League on Sunday.
"It feels good," she told Chelsea's website. "I am really happy but a lot of relief. It's been a long journey and I'm glad it's over."
Scoring her 100th goal for Chelsea made the return even more special.
"To do it for such a massive club, and a club I love so dearly, is a massive achievement and something I am really proud of," she added.
"I don't reflect too much on my goals, but to score 100 for Chelsea is something I will keep with me forever."
Kerr has won five league titles, three FA Cups and two League Cups since making her Chelsea debut in 2020, and manager Sonia Bompastor underlined her importance to the club.
"You know what Sam represents for Chelsea. For me, she's an idol," said the Frenchwoman.
"She doesn't like being in front of everyone and getting the limelight, but she really deserves it. I think she needs to enjoy it as well because she's been through tough moments."