The person spoke on the condition of anonymity because Andrews has not made his announcement. Andrews called an 11:30 a.m. news conference at his district office in Haddon Heights.
The 56-year-old was first elected to Congress to represent a district outside Philadelphia in 1990. He intends to join a law firm with offices in Washington as a senior partner.
A congressional ethics committee has been looking into Andrews' spending after reports more than two years ago that he was using campaign funds for frequent trips to California, where his daughter had a fledgling singing and acting career.
Bill Caruso, a former aide to Andrews, said he believes Andrews' decision to resign now came largely because both his daughters are in college. "It has everything to do with the opportunity," Caruso said.
Melanie Sloan, executive director of Citizens for Responsibility and Ethics in Washington, a watchdog group that has long criticized Andrews' campaign spending practices, said his resignation would mean that the House Ethics Committee investigation would be closed.
"I hope in this instance, the ethics committee will release its findings," she said. "Andrews, who seems to have been engaged in serious wrongdoing should not be able walk into a cushy high-paid job without Americans knowing about his self-dealing."
Andrews' campaign manager in the past has criticized Sloan's organization as "shadowy."
The seat will be open until the general election in November.
For years, Andrews was seen - and saw himself - as a politician capable of higher office.
He ran statewide twice, losing a gubernatorial primary in 1997 and then mounting an unsuccessful and brazen primary challenge in 2008 against U.S. Sen. Frank Lautenberg, suggesting that Lautenberg was too old for the job.
The challenge against Lautenberg, who died last year at 89, ruffled the feathers of some in New Jersey's Democratic establishment.
Andrews, who grew up in the blue-collar town of Bellmawr and commutes daily by train to Washington, said he would not return to Congress if he lost that election. His wife ran in the primary for the seat that year and won. But after Andrews' primary loss, he returned to the ballot for the general election.
Andrews has been in elective office nearly his entire adult life, serving as a Camden County freeholder before he was elected to serve New Jersey's 1st Congressional District, an area dominated by Democrats, at 33.
He's been known as one of the most independent Democrats in New Jersey's Congressional delegation. He broke with his party on support for the war in Iraq, even working with the George W. Bush White House on the wording of the resolution authorizing military action.
He also had a key role passing President Barack Obama's health insurance overhaul in 2010.
In recent years, Andrews has attracted scrutiny for campaign spending practices.
In 2009, he repaid his campaign for more than $900 for replacing clothing that was lost by an airline. The Federal Election Commission had ruled that that expenditure was not permissible.
In 2011, he reimbursed more than $13,000 he used to take his family to a donor's wedding in Scotland. Even as it repaid, the campaign said there was nothing wrong with using campaign money for the trip.
He is also being investigated for using campaign money to travel to California. An Associated Press analysis of his campaign spending in 2012 found he had spent at least $97,000 in campaign funds on at least 18 trips to California from 2007 to 2011.
At least a few of those trips coincided with times his daughter Josie was working there. His campaign defended the travel, saying he raised money there, made connections to key fundraisers and gathered information on issues he was interested in.
His will be the second New Jersey congressional seat open for this November's election.
Rep. Jon Runyan, a Republican who represents neighboring 3rd District, stretching from the Philadelphia suburbs to the shore, has announced that he will not seek a third term.
Mulvihill reported from Haddonfield, N.J.