Coyle was formerly head of the HR business partner team. She moved to the interim London HR director role in August when the previous incumbent left the firm.
From Monday 22 September, Coyle is officially permanent in the post.
She told HR magazine "driving the implementation of clear and ambitious strategy" at the company is a key aim in her new role.
"It's important we maintain our position as one of the top employers in the UK," she said. "We can do this through focusing on morale, motivation and retention, as well as attracting high quality candidates. Driving higher organisational performance as well as maintaining our strong employer branding is a challenge but I'm excited I have the opportunity to take it on."
Coyle will also sit on the law firm's eight-person London management committee, meaning that the ratio of men and women will be 50/50.
London managing partner Paul Rawlinson described Coyle as a "first-class HR practitioner".
"I am confident she will continue to drive the firm's reputation as an employer of choice and I look forward to working closely with her on the management committee," he added.
