After helping to secure a second term for President Bush, Republican National Committee Chairman Ed Gillespie plans to give up his post by year’s end and return to the Washington lobbying shop he helped found four years ago, according to Republican Party officials and lobbyists at the firm.

Bush campaign manager Ken Mehlman is widely expected to succeed Gillespie at the helm of the RNC, according to party officials.

Gillespie “has always said that he intends to return to the firm” after completing an election-year term with the RNC, said Jack Quinn, the Democrat who co-founded Quinn Gillespie & Associates with Gillespie.

But Quinn said he and Gillespie have not discussed the timing of the move.

“Ed has earned and deserves a break,” Quinn said, so “we haven’t focused on a particular date.”

The RNC will install Gillespie’s successor at its annual meeting in January, though Gillespie could return to his lobbying practice sooner.

At least his office is available. Last weekend, former Bush spokesman Ari Fleischer moved out of Gillespie’s Connecticut Avenue office, where he had temporarily based his one-man communications shop.

While Gillespie’s return provides a boost to Quinn Gillespie & Associates, the firm benefited from his reflected glory at the RNC: It added a bit of business during Gillespie’s absence, rather than seeing receipts drop off.

In the six months before Gillespie left his firm to take the RNC post, the firm booked $6.3 million in lobbying revenue, according to disclosure records. In the same period this year — while Gillespie was crisscrossing the country on behalf of Bush and other Republican candidates — the firm earned $6.4 million in lobbying revenue.

The firm was able to weather Gillespie’s departure because few of its clients departed.

“One of the things that we are most proud of is that, with very rare exceptions, the clients keep coming back,” Quinn said.

Among the clients that ended their lobbying contracts with Quinn Gillespie & Associates in the last year were Verisign and the American Insurance Association.

But the firm inked new deals with EADS North America and Genworth Financial.

Quinn credited its success in Gillespie’s absence to the firm’s strong bipartisan roots.

“We never lost a wink of sleep over the hypothesizing what the effect of the election outcome might be on the firm,” Quinn said. “We have a great group of Republicans and a fantastic group of Democrats.”