She added that she is “very happy to be staying”.
“This is a place where I can still continue to grow, develop and be challenged,” she said.
“As a group, we’re all very focused on bringing more silverware to this club and I can’t wait to get started again when the new season comes around.”
Williamson, who previously signed a new deal with Arsenal in 2022, has re-established herself as a key player for Arsenal since suffering a knee ligament injury which ruled her out of the 2023 Women’s World Cup.
She follows fellow senior player Stina Blackstenius in prolonging her stay at the Gunners, although Vivianne Miedema has played her final game for the club after the Gunners decided not to renew her contract.
Arsenal head coach Jonas Eidevall said: “Leah is an essential part of our team so we’re delighted she has signed a new contract with us. She brings us so much on and off the pitch – leadership, accountability and commitment.
“Leah has a special bond with Arsenal and I’m looking forward to continuing to work together to bring more success to this great club.”
Arsenal have not specified the length of Williamson’s new contract, but confirmed to BBC Sport that it is a “multiple-year” deal.