He fills the job left vacant when former GC Timothy Mayopoulos was promoted in June to be Fannie Mae's president and chief executive officer.
Lerman, 56, was Pfizer's associate general counsel and chief litigation counsel, responsible for leading the company's product and commercial litigation, government investigations and patent litigation teams.
Before he joined Pfizer in late 2008, he was a partner at Winston & Strawn, where he was co-chair of the firm's white collar practice. His clients included former Illinois Governor Rod Blagojevich.
Lerman is also a former partner at Kirkland & Ellis, and was a federal prosecutor in the Northern District of Illinois from 1986 to 1994.
"Brad has extraordinary experience and he will be a great addition to our team," Mayopoulos said in a news release. "Brad has integrity, excellent leadership skills and a proven track record in achieving positive outcomes for corporations across a broad spectrum of legal specialties."
Judith Dunn, who had been the principal deputy general counsel, is serving as interim general counsel.
Lerman's appointment comes two months after Fannie Mae sibling Freddie Mac announced it had a new general counsel — William McDavid, a former top lawyer at J.P. Morgan Chase & Co.