After serving for four decades in Congress, Rep. Henry Waxman, a prominent Democrat known for his work on healthcare, the environment and government oversight, announced his plans today to retire at the end of this year.

"I have had a long career and an eventful one - and I wouldn't trade any of it," Waxman said in a statement. "After 40 years in Congress, it's time for someone else to have the chance to make his or her mark."

Waxman's announcement is the seventh retirement for Democrats during this election cycle in the House, a chamber where Democrats' hopes of retaking a majority seem to be falling out of reach.

But Waxman's district, in Los Angeles, is heavily Democratic, and Rep. Greg Walden, chairman of the Republican Congressional campaign committee, said he doesn't anticipate a competitive race to replace Waxman.

Waxman's announcement comes on the heels of retirements from other long-standing Democrats, like fellow 20-term California Rep. George Miller, Virginia's Rep. James Moran and New York's Carolyn McCarthy.

But the Republicans are losing more representatives to retirement than the Democrats: 10 members of Congress, including Minnesota's Michele Bachmann and Virginia's Frank Wolf, have decided to leave their posts.

Minority Leader Rep. Nancy Pelosi, one of Waxman's close allies in the House, praised Waxman for his leadership and his service.

"For the past four decades, Congressman Henry Waxman's name has been synonymous with responsible action, extraordinary legislative skill, passionate public service, and bold leadership on behalf of Los Angeles, California, and the American people," Pelosi said in a statement.

"It has been a true privilege to call him colleague and a distinct honor to know him as a friend," she said.

One of the longest-serving sitting members of Congress, Waxman was first elected to the House in 1974 after working as a lawyer and serving in the California state legislature.

In Congress, Waxman made an impact on the pharmaceutical market and the tobacco industry. He also led the fight to expand Medicaid and has pushed for environmental regulations like the Clean Air Act and limits on carbon emission reductions.

" I hoped to be able to serve 20 years and leave a mark on some important issues," Waxman said. "I never imagined I would be in the House for 40 years and be able to advance every issue I care deeply about."

Waxman is also known for his work on governmental oversight, leading hearings on everything from steroids in baseball to the economic recession of the past few years.