Randy Mastro, lawyer for Chevron and Chris Christie, joins King & Spalding

Attorney Randy Mastro arrives for a news conference to announce the findings of an independent review of New Jersey Govornor Chris Christie’s governance in New York, March 27, 2014. REUTERS/Brendan McDermid

(Reuters) – Randy Mastro, a prominent trial lawyer and former New York deputy mayor whose clients have included AIG, Chevron, DraftKings and former New Jersey Governor Chris Christie, is joining law firm King & Spalding after leading the litigation practice at Gibson, Dunn & Crutcher for more than 20 years.

Mastro said Wednesday that his decision to leave was partly in response to Gibson Dunn’s mandatory retirement age for equity partners, which is 68. Mastro is 65.

He said he could have kept practicing at Gibson Dunn once he turned 68, but on a fixed compensation basis. Equity partners at law firm take a share of profits.

Mastro said he had also aged out of Gibson Dunn’s executive committee when he turned 65, requiring him to step down from that role last year.

King & Spalding, where he is joining as a partner in New York next week, doesn’t have a mandatory retirement age, Mastro said. He said he is not slowing down his legal career and eager to help King & Spalding continue building its presence in the city.

“The horizon is up, up and up,” Mastro said. “I plan to practice for a long, long time.”

Gibson Dunn chair and managing partner Barbara Becker thanked Mastro for his contributions and wished him well in a statement. She said Gibson Dunn’s “powerhouse litigation practice has never been stronger, in New York and across the firm.”

At Gibson Dunn, Mastro took the lead for Chevron in U.S. litigation over the fate of a $9.5 billion environmental judgment against the oil giant in Ecuador, persuading a federal judge in New York that the award was obtained by fraud.

Mastro and Gibson Dunn were hired by Christie in 2014 to investigate whether any laws were broken when a top Christie aide ordered seemingly politically motivated traffic jams at the George Washington Bridge. Mastro and the firm cleared Christie of wrongdoing.

In both cases, Mastro said he worked with King & Spalding. King & Spalding represented Chevron in international arbitration against the Ecudorian government. Former King & Spalding partner Christopher Wray, now the director of the FBI, represented Christie during the Bridgegate scandal.

From 1994 to 1998, Mastro served as chief of staff and deputy mayor for operations for then-New York City Mayor Rudy Giuliani.

Los Angeles-founded Gibson Dunn and Atlanta-founded King & Spalding have had similar growth rates over the last two decades, with both firms substantially expanding their revenues and lawyer head counts.

Gibson Dunn generated $2.4 billion in revenue with more than 1,500 lawyers last year, according to The American Lawyer, while King & Spalding brought in $1.8 billion with more than 1,200 lawyers.

(NOTE: This story has been updated with comments from Randy Mastro and Barbara Becker.)

Read more:

FBI director nominee Wray earned $9.2 million in law practice last year

U.S. judge rules for Chevron in Ecuador environmental case

New Jersey governor hires outside law firm in bridge probe

Our Standards: The Thomson Reuters Trust Principles.