Nossaman Guthner Knox & Elliott LLP plans to merge with O'Connor & Hannan LLP.

O'Connor & Hannan LLP, a D.C.-based firm with 23 attorneys and lobbyists at 1666 K St. NW, will rename as Nossaman LLP/O'Connor & Hannan and have more than 150 attorneys and lobbyists in eight offices. The merger takes effect Tuesday.

Los Angeles-based Nossaman will add D.C. to its list of locations, which includes Arlington County and offices in Austin, Texas, and a handful of cities in California.

Recently brought together through several joint new business proposals, the two firms found similarities in environmental law, government relations and infrastructure.

"The attorneys joining Nossaman add another dimension to our core practice areas and to the services we can offer our clients at the federal level," said Michael Heumann, managing partner at Nossaman. "We are further differentiating ourselves from other mid-sized California law firms and offering our clients something new."

Next month, Nossaman's D.C. office will elect members to the firm's executive and compensation committees.

Timothy Jenkins, a legislative advocate with 51-year-old O'Connor & Hannan, will become chairman of Nossaman's national government relations practice group.