"You voted loudly and clearly for change, and you have entrusted us with what may be our last, best hope for a stronger New Jersey the New Jersey of our youth, full of hope and opportunity,'' Christie said in his inaugural address. "New Jersey, you voted for change and today change has arrived.''
Christie, takes over a state plagued by the nation's highest taxes, a deficit that could hit $10 billion by July and unemployment near 10 percent.
Christie's swearing in marked another reminder of President Barack Obama's vulnerability on the same day another Northeastern election could derail parts of his agenda.
On Tuesday, Democrats nervously watched the Senate contest in Massachusetts where Republican Scott Brown threatened to take the seat held by the late Edward Kennedy. Obama campaigned for Democrat Martha Coakley and a loss would break the Democrats' filibuster-proof 60 vote majority in the Senate.
Obama and Vice President Joe Biden had campaigned for Gov. Jon Corzine in the fall, but it wasn't enough for him to beat Christie. The loss was the first blow to Obama, followed by a Republican in Virginia winning the only other governor's race in November.
Christie, a 47-year-old former federal prosecutor, ran on a platform of smaller government and took shots at Corzine, a former Wall Street executive, for what he called poor economic stewardship. But Christie was criticized during the campaign for remaining vague about how he would solve New Jersey's chronic fiscal problems.
He seized on the dual themes of voter discontent and change in his 33-minute inaugural address.
"Rarely in New Jersey's history have we faced the challenges we face today,'' Christie said. "There is fear and uncertainty. But fear and uncertainty are not necessary and do not have to be permanent. We have the tools for a brighter future, if we change direction.''
Corzine was on hand to witness his successor take the oath of office. Former Govs. Brendan Byrne, Tom Kean Sr., Christie Whitman, Jim Florio, Don DiFrancesco and Dick Codey also were in the front row.
Christie takes charge of a government dominated by Democrats waiting to see exactly how he will balance the budget without breaking his campaign pledge to not raise taxes and to roll back others. New Jersey homeowners pay the nation's highest taxes, an average of $7,045 a year.
At a Mass Tuesday morning at the Cathedral Basilica of the Sacred Heart in Newark, Archbishop John Myers said Christie will need the wisdom of Solomon.
Donald Trump also attended the Mass in Newark, Christie's birthplace.
"He's going to be a great governor, which New Jersey could use. He will go down as the best governor there is,'' Trump said, adding that the two had been friends for a long time.
After the swearing in, Christie and Guadagno were heading to the governor's mansion in Princeton for a private lunch. An evening cocktail reception at the Prudential Center in Newark was planned.