Leiv represents clients in complex antitrust investigations and litigation, including matters involving price fixing and monopolization. In addition, he has extensive experience handling class actions, multi-party litigation, and mergers and acquisitions. Leiv has argued matters before the federal and state courts, the Federal Trade Commission, and the Department of Justice, among other administrative agencies.

His experience ranges across industries and he is particularly well-versed in defending clients in the pharmaceutical and financial services industries, both of which have been the subject of government scrutiny for pricing practices. He is known for his ability to wade through dense statutes and contradictory guidance to achieve success for his clients in government and private antitrust matters.

A leader among his peers, Leiv was a partner at three global firms before joining Lowenstein. He recently served as co-chair of the antitrust, competition, and trade regulation practice at one global firm.