The surprise move upends both state and national political worlds. At the same time, it allows Christie to avoid the fraught terrain of having to appoint an interim lawmaker to serve through the upcoming debates in Washington on topics like immigration reform.
"The gun has been fired. It's time to go," Christie told reporters during an afternoon news conference at his office in the Trenton statehouse. "I firmly believe that the decisions that need to be made in Washington are too great to be made by an appointee for a period of 18 months."
Christie will still get to appoint an interim senator to serve until October, though he said he had not decided yet who that would be.
The special election is going to be held on Oct. 16, three weeks before the governor stands for his own re-election on Nov. 5.
The decision to hold an election in October comes with a price tag approaching $25 million because every statewide election in New Jersey costs more than $12 million to execute, and the two parties will hold primaries before the election.
Christie tried to head off criticism of the expense.
"I don't know what the cost is and I, quite frankly, don't care," Christie said. "I don't think you can put a price tag on what it's worth to have an elected person in the United States Senate and I will do whatever I need to do to make sure those costs are covered because all the people of the state of New Jersey will benefit from it and we're not going to be penny-wise and pound-foolish around here."
But critics quickly pounced on the cost.
American Bridge 21st Century issued a list of "What else could New Jersey use $12 million for." Among the items cited: two months of food bank and soup kitchen assistance for areas affected by Superstorm Sandy; and the restoration of "over half of Christie's cuts to medical services for the elderly."
The two political parties would have to hold primaries scheduled for Aug. 13 to pick candidates to run in the special election. The winner of the October contest would serve through the end of 2014. A second election for the full six-year Senate term is to be held in November 2014.
Criticism also came from Dick Armey, former tea House majority leader and one-time power in the tea party movement. Armey, a Texas Republican, said Christie was "committing a big mistake" that will anger Republicans throughout the state and the country and could have reverberations through 2016.
Armey said despite the New Jersey governor stressing "fiscal austerity, fiscal responsibility, small government" he is spending what could be $25 million, something he says conservative Republicans will see as a waste.
"He violated the first principal of politics: never sacrifice the friend you already have for the friend you will never have," Armey told ABC News. "I characterize it as debilitating stupidity."
Armey points out that Christie already "angered a lot of conservatives" after superstorm Sandy when he "paraded with Obama and he made a bit of a horse's rear of himself," but said that now even base Republicans in New Jersey could fail to show up in 2013 for his gubernatorial re-election bid.
"Any hope that this governor has of running for president is gone. It's over," said Armey, who claims Christie has " been Obama's best friend for the last year and a half." He predicted Christie will have to depend on Democrats to back him in his gubernatorial re-elect. "That's not the kind of calculus that says you can win a Republican nomination two years later."
Lautenberg, a five-term liberal who was the Senate's last World War II veteran, died of pneumonia on Monday. He had been in declining health since being diagnosed with cancer three years ago. A funeral is to be held Wednesday in Manhattan. The senator's body will then be taken to Washington, where he is to lie in repose at the Capitol Thursday.
Today's announcement came after 24 hours of serious internal discussions over the governor's complicated options for replacing Lautenberg.
Two people briefed on the deliberations said the debate raged until only minutes before Christie took to the microphone.
"This is happening so quickly," one source told ABC News in the minutes before the governor spoke.
Behind closed doors, Christie and his aides took the cost of the elections seriously, the sources said. But they eventually decided to go with the expedited schedule and take the political hit on spending millions in a financially strapped state where property taxes are through the roof and residents have long clamored for relief.
Gov. Christie Sets October Special Election
Other options Christie considered included merging the special Senate election with his own re-election this November, or waiting until November 2014 when the regular Senate election is scheduled. He told reporters the later date was not fair to voters.
As for the earlier date, Christie was coy when asked why he did not choose that option. But members of his inner circle have not been shy in the last 24 hours in telling ABC News that the governor simply would not countenance a November 2013 special Senate race that would end up placing the Senate candidates – possibly among them Newark Mayor Cory Booker – on top of him on the state's ballots. Federal offices must appear higher than state positions on New Jersey ballot.
New Jersey county clerks, who run the elections and are politically powerful on their own, could object to an October election. Already some are telling reporters that the August primary would make it hard for them to meet the Aug. 28 deadline for distributing ballots to active-duty members of the military. And there are concerns that if the October election is contested, it could interfere with the November general election.
Christie's announcement comes, coincidentally, on New Jersey's regular primary day when he is to be officially named the Republican nominee for governor. Christie is going to face off against state Sen. Barbara Buono in November.
Christie has a huge lead in the governor's race and national party leaders were expecting the campaign to draw little national attention or money because it had become such a yawner.
"All of you who are bored with the governor's race, I've solved your problem," Christie said.