Maxwell, who played DI Sam Nixon, will depart the show in an "explosive storyline", reports The Sun.
"I've loved every minute of my seven years on The Bill but feel I have taken the character of Sam as far as I can," she said. "It is time to move on to new challenges.
"When people start referring to you as the longest-standing female cast member it is probably time to take the hint."
Earlier this month, ITV’s director of television Peter Fincham revealed that the long-running series' output was being reduced to just one episode a week. The relaunched show will air after 9pm and has been described as "grittier and more action-packed".