A longtime Jones Day partner in Washington who had been co-leader of the firm’s energy practice was sworn in Thursday as chairman of the Federal Energy Regulatory Commission.

Kevin McIntyre, a Jones Day lawyer since 1999, represented energy companies facing regulatory, compliance and enforcement challenges. Former clients included St. Louis-based Ameren Corp., Chicago’s Lakeside Energy LLC and TECO Energy Inc. of Tampa, Florida, according to McIntyre’s financial disclosure released by the U.S. Office of Government Ethics.