But with younger candidates already announcing their intention to run for his seat, Lautenberg said it was time to open the door to others.
"I will have been here 30 years when I finish two years hence and . . . I think that the time was right," he said. "It was nothing other than clear decision making."
A possible primary challenge did not affect his decision - despite polls showing Newark Mayor Cory Booker, who stated his intention to run in December, as the heavy favorite in a potential match up.
"I leave here feeling good about the contributions that I've been able to make," Lautenberg said.
As he spoke, U.S. Sen. Chuck Schumer (D., N.Y.) walked by and clapped Lautenberg on the shoulders. "He's the greatest; we're going to miss him," Schumer said.
Democrats in Trenton and Washington showered Lautenberg with praise Thursday, calling him "a lion of the Democratic Party" whose work on public health and safety issues changed life in America.
Even President Obama lauded the senator.
"Frank is a steadfast champion of the people of New Jersey," Obama said in a statement. "Throughout his time in the Senate, Frank has fought tirelessly for workers, veterans, members of our military and their families, and immigrants, and he continues to make extraordinary contributions to our nation's safety, and the health and welfare of our citizens."Republican Sen. John McCain of Arizona noted that Lautenberg is the last World War II veteran in Congress.
Lautenberg is one of the Senate's most liberal members. His landmark legislation includes banning smoking on airplanes, setting a national blood-alcohol limit of .08 for drunk driving, and forbidding those convicted of domestic violence crimes from possessing a firearm.
"When the history books are written, Frank Lautenberg will be remembered as a tenacious fighter for not only the people of New Jersey but literally the people of our country," said State Assemblyman John Wisniewski, chairman of the New Jersey Democratic State Committee. "He has taken his humble origins and he always remembered that when voting on legislation.
Although Gov. Christie is up for reelection this year, the 2014 Senate race grabbed the limelight in December when Booker said he wanted to run for Lautenberg's seat.
State Democrats had hoped that Booker, 43, would take on popular Christie in the gubernatorial race this year. Booker has become a national figure through his massive Twitter following, his hands-on governing style (he digs out cars during snowstorms and he recently sheltered a dog left in the cold), and his heroics (he ran into a burning building to save his neighbor).
Booker's announcement riled Lautenberg, who, in keeping with his reputation as a scrappy outsider with a sharp tongue, chided the mayor for getting ahead of himself.
He even joked that he would "spank" Booker.
"I have four children, I love each one of them. I can't tell you that one of them wasn't occasionally disrespectful, so I gave them a spanking and everything was OK," Lautenberg told The Inquirer.
But Lautenberg indicated on Thursday that he doesn't hold a grudge.
He declined to endorse any potential successors and noted that there are several potentially strong candidates from the U.S. House who may be interested in the Senate seat.
Booker spoke only accolades about Lautenberg on Thursday. He said the elder senator was a "strong model of leadership and service."
"Here in Newark, his tireless advocacy and numerous contributions have helped our city endure difficult days and are now fueling our turn toward growth, promise and endless possibility," Booker said. "Newarkers know, from our airport and the roads we drive on to our schools and services for our seniors, Frank Lautenberg has helped empower people and strengthen our city."
Christie, who has battled with Lautenberg since he became governor in 2010, said he owed the senator for his help in recent months.
"I will always be grateful for his doggedness in fighting with me and the delegation to ensure congressional passage of an aid package after Hurricane Sandy that is delivering necessary assistance to our residents," Christie said in a statement.
State Senate President Stephen Sweeney (D., Gloucester) and Assembly Speaker Sheila Oliver (D., Essex) are both considering a run for Lautenberg's seat. U.S. Rep. Frank Pallone (D., N.J.) is considered a likely opponent, although he has not announced his intentions.
U.S. Rep. Rob Andrews (D., N.J.), who ran in a primary against Lautenberg in 2008, said it's "extremely unlikely" that he would run for Senate again, though he did not rule it out, saying "you never say never."
"I would rather be in a leadership position in the House than a freshman in the Senate," Andrews said.
Unlike many politicians, Lautenberg didn't come up through the party ranks.He grew up in the working-class city of Paterson, the son of Russian and Polish immigrants. His father, who died when Lautenberg was 19, worked in a silk mill.
Lautenberg served in the U.S. Army Signal Corps during World War II, went to Columbia University on the GI Bill, and started a company with two friends after graduation. The business, Automatic Data Processing, or ADP, was the nation's first payroll-services company. The company went public in 1961 and made Lautenberg rich: Lautenberg's net worth as of 2010 was valued at more than $40 million, according to the 2010 Almanac of American Politics.
Lautenberg has had a hand in politics long enough to have been on President Nixon's "enemies list"; he'd donated $90,000 to George McGovern, the Democratic presidential candidate in 1972.
But he didn't jump into the fray himself until 1982, when, at 58, he decided to run for an open U.S. Senate seat.
He'd never been elected to office. He was serving his fourth year on the New York and New Jersey Port Authority Commission.
But that year the Abscam bribery scandal churned the New Jersey political world. Democratic U.S. Sen. Harrison William resigned before the chamber could expel him.
Lautenberg poured $5 million into the race, narrowly defeating two-term Republican U.S. Rep. Millicent Fenwick, a colorful and independent member of the House who refused donations corporations or political action committee. Although Lautenberg chafed at the accusation that he made a campaign issue of Fenwick's age - she was then 72 - political historians say he painted her as an eccentric out of touch with New Jerseyans and questioned her "fitness" to do the job.
Lautenberg won 51 percent to 48 percent of the vote.
Last year, Lautenberg said that he would run for reelection in 2014. In an April interview, he struck a defiant tone: "I won't be flushed out and I won't be pushed out," he said following a discussion at Rider University.
But in recent months, speculation that Lautenberg would step aside grew.
On Thursday, Assembly Speaker Sheila Oliver (D., Essex) in an interview between votes on the Assembly floor, wished Lautenberg well, calling him "one of the lions of the Democratic party on Capitol Hill."
She also reiterated that Booker is not the only possible candidate.
"No one owns an elected seat," she said. "It has nothing to do with your national reputation, it has nothing to do with how many Twitter followers you have."
Lautenberg, a longtime advocate for tougher gun laws, said he plans to keep fighting to push a new set of restrictions. He also plans to spend more time with his wife and 10 grandchildren.
Contact Joelle Farrell at 856-779-3237 or firstname.lastname@example.org or on Twitter at @joellefarrell.