By tradition since the 1947 state constitution, the seven member New Jersey Supreme Court maintains a political balance and is composed of four members of either the Democratic Party or Republican Party and three of the other. Christie broke with the tradition in May 2010 when he chose not to renominate Justice John E. Wallace Jr. Christie had said the court "had inappropriately encroached on both the executive and legislative function, and that if elected governor, I would take steps through the decisions I made regarding the court to bring back an appropriate constitutional balance to the court." Since taking office, Christie has been in a major conflict with the New Jersey Legislature over the court's partisan balance. The stand-off between the governor and the New Jersey Senate has resulted in longstanding vacancies, with temporarily assigned appellate judges filling in.

Christie was born in Newark, New Jersey, to Sondra A. (née Grasso), a telephone receptionist, and Wilbur James "Bill" Christie, a certified public accountant. His mother was of Italian (Sicilian) ancestry, and father is of German, Scottish, and Irish descent. Christie's family moved to Livingston, New Jersey, after the 1967 Newark riots, and Christie lived there until he graduated from Livingston High School in 1980. At Livingston High School, Christie served as class President and played catcher for the baseball team.

Christie's father and mother were Republican and Democratic, respectively. He has credited, however, his Democratic-leaning mother for indirectly making him a Republican by encouraging him in 1977 to volunteer for the gubernatorial candidate who became his role model: Tom Kean. Christie had become interested in Kean after the Politician, then a state legislator, spoke to Christie's junior high school class.

Continuing the tradition of earlier New Jersey governors since the 1980s, Christie traveled to Israel in April 2012. During the visit, which included meetings with Prime Minister Benjamin Netanyahu and President Shimon Peres, Christie commented that "Jerusalem has never been better or freer than under Israeli control." Christie took a helicopter tour of the West Bank and cautioned against Israeli withdrawal from the West Bank, Jerusalem or the Golan Heights. The official title given to the trip was "Jersey to Jerusalem Trade Mission: Economic Growth, Diplomacy, Observance". The visit to Israel was Christie's first official overseas trip since taking office. From Israel, Christie continued with his family to Jordan, as guests of King Abdullah II.

Christie graduated from the University of Delaware with a Bachelor of Arts in political science in 1984 and Seton Hall University School of Law with a J.D. in 1987. He was admitted to the New Jersey State Bar Association and the Bar of the United States District Court, District of New Jersey, in December 1987. He was awarded honorary doctorate degrees by Rutgers University and Monmouth University in 2010.

In 1986, Christie married Mary Pat Foster, a fellow student at the University of Delaware. After marrying, they shared a studio apartment in Summit, New Jersey. Mary Pat Christie pursued a career in investment banking and eventually worked at the Wall Street firm Cantor Fitzgerald; she left the firm in 2001 following the September 11 attacks. Through April 2015 she was a managing Director at the Wall Street investment firm Angelo, Gordon & Co.

In 1987, Christie joined the law firm of Dughi, Hewit & Palatucci of Cranford, New Jersey. In 1993, he was named a partner in the firm. Christie specialized in securities law, appellate practice, election law, and government affairs. He is a member of the American Bar Association and the New Jersey State Bar Association and was a member of the Election Law Committee of the New Jersey State Bar Association. From 1999 to 2001, Christie was registered statehouse lobbyist for Dughi and Hewit.

Christie volunteered for President George H. W. Bush's 1992 re-election campaign in New Jersey, and became close to Bush's state Director, Bill Palatucci. Following the campaign, Christie decided to run for office, and moved to Mendham Township. In 1993, Christie launched a primary challenge against the New Jersey Senate Majority Leader, John H. Dorsey. However, Christie's campaign ended after Dorsey successfully challenged the validity of Christie's petition to appear on the ballot.

In 1994, Christie was elected as a Republican to the Board of Chosen Freeholders, or legislators, for Morris County, New Jersey, after he and a running mate defeated incumbent freeholders in the party primary. Following the election, the defeated incumbents filed a defamation lawsuit against Christie based on statements made during the primary campaign. Christie had incorrectly stated that the incumbents were under "investigation" for violating certain local laws. The lawsuit was settled out of court, with Christie acknowledging that the prosecutor had actually convened an "inquiry" instead of an "investigation", and apologizing for the error, which he said was unintentional.

In 1995, Christie announced a bid for a seat in the New Jersey General Assembly; he and attorney Rick Merkt ran as a ticket against incumbent Assemblyman Anthony Bucco and attorney Michael Patrick Carroll in the Republican primary. Christie ran as a pro-choice candidate and supporter of the ban on assault weapons. Bucco and Carroll, the establishment candidates, defeated the up-and-comers by a wide margin. After this loss, Christie's bid for re-nomination to the freeholder board was unlikely, as unhappy Republicans recruited John J. Murphy to run against Christie in 1997. Murphy defeated Christie in the primary. Murphy, who had falsely accused Christie of having the county pay his legal bills in the architect's lawsuit, was sued by Christie after the election. They settled out of court with the Freeholders admitting wrongdoing and apologizing. Christie's career in Morris County politics was over by 1998.

Christie has been critical about section 287(g) of the Immigration and Nationality Act, enacted in 1996, which can be used to grant local law enforcement officers power to perform immigration law enforcement functions.

When Christie's part-time position as a Chosen Freeholder lapsed, he returned full attention to his law firm Dughi, Hewit & Palatucci. Alongside fellow partner and later, gubernatorial campaign fundraiser Bill Palatucci, Christie's firm opened an office in the state capital, Trenton, devoted mainly to lobbying. Between 1999 and 2001, Christie and Palatucci lobbied on behalf of, among others, GPU Energy for deregulation of New Jersey's electric and gas industry; the Securities Industry Association to block the inclusion of securities fraud under the state's Consumer Fraud Act; Hackensack University Medical Center for state grants; and the University of Phoenix for a New Jersey higher education license. During the 2000 presidential election, Christie was George W. Bush's campaign Lawyer for the state of New Jersey.

On December 7, 2001, President George W. Bush appointed Christie the U.S. Attorney for the District of New Jersey. Some members of the New Jersey Bar professed disappointment at Christie's lack of experience. At the time, he had never practiced in a federal courtroom before, and had little experience in Criminal law. Christie received the overwhelming support of the Republican Party in New Jersey. A spokesperson for Acting Governor Donald DiFrancesco, who selected nominees for the position, said that he received hundreds of letters of support for Christie "from everyone from the Assembly speaker down to the county level, close to every member of the Legislature and every county chairman." Christie was also a top fundraiser for Bush's 2000 presidential campaign. He helped raise $350,000 for Bush, qualifying him as a "Pioneer", and also donated to DiFrancesco. Democrats seized upon the role played by Bush's political adviser, Karl Rove, after Christie's law partner, william Palatucci, a Republican political consultant and Bush supporter, boasted that he had selected a United States attorney by forwarding Christie's résumé to Rove. According to New Jersey's senior Senator, Bob Torricelli, Christie promised to appoint a "professional" with federal courtroom experience as deputy if confirmed. By Senate tradition, if a state's senior Senator opposes the nomination of a U.S. Attorney, the nomination is effectively dead, but Christie's promise was enough for Torricelli to give the nomination his blessing. He was unanimously confirmed by the United States Senate on December 20, 2001, and sworn into office on January 17, 2002.

Christie negotiated seven deal deferred prosecution agreements (DPAs) during his tenure, some of which were controversial. Under agreements like these, corporations avoid prosecution if they promise not just to obey the law or pay for bad acts, but also promise to change personnel, or revamp Business practices, or adopt new types of corporate governance. They are typically used in lieu of prosecution when there is evidence of particularly egregious corporate misconduct. Since 2002, these types of agreements have been sharply on the rise among federal prosecutors, with 23 between 2002 and 2005, and 66 between 2006 and 2008. Outside monitors are appointed in about half of all DPAs, to make sure that the corporations comply. In one case, Christie recommended appointment of The Ashcroft Group, a consulting firm owned by his former boss John Ashcroft, as an outside monitor of Zimmer Holdings—a contract worth as much as $52 million from Zimmer, which was an amount in line with fee structures at that time. In another instance, Christie's office deferred Criminal prosecution of pharmaceutical company Bristol Myers in a deal that required the company to dedicate $5 million for a Business ethics chair at Seton Hall University School of Law, Christie's alma mater.

Besides doubling the size of the anticorruption unit for New Jersey, Christie also prosecuted other federal crimes. For Example, he obtained convictions of brothel owners who kept Mexican teenagers in slavery as prostitutes, convicted 42 gang members of the Double II Set of various crimes including more than 25 murders, and convicted British trader Hemant Lakhani of trying to sell missiles. Despite claims of entrapment, Lakhani was convicted by jury in April 2005 of attempting to provide material support to terrorists, unlawful brokering of foreign defense articles, and attempting to import merchandise into the U.S. by means of false statements, plus two counts of money laundering. He was sentenced to 47 years in prison.

In 2007, Christie prosecuted the planners of the averted 2007 Fort Dix attack plot, which he has frequently mentioned as a career highlight.

Christie has said that each state has the right to determine firearms laws without federal interference. When announcing his candidacy in 2009 he said he supported aggressive enforcement of the state's current gun laws. In 2013, he chose not to defend a legal challenge to a New Jersey law requiring individuals to prove an urgent threat of violence before getting permits to carry handguns. In July 2014, Christie vetoed legislation that would have reduced the allowed legal size of ammunition magazines. Instead he re-wrote it, proposing a new standard for involuntary commitment of people who are not necessarily deemed dangerous "but whose mental illness, if untreated, could deteriorate to the point of harm" as well as other forms of involuntary mental health treatments. Christie had previously vetoed proposed legislation that would bar the state pension fund from investing in companies that manufacture or sell assault firearms for civilian use and a bill to prohibit the sale of .50-caliber rifles to civilians. In July 2015, Christie vetoed a bill passed the Assembly by a 74–0 (six abstentions) and the Senate by a 38–0 (2 abstentions) which would require anyone seeking to have their mental health records expunged to purchase a firearm to notify the State Police, their county prosecutor and their local police department when petitioning the court. In October 2015, the New Jersey Senate voted to override Christie's veto.

In 2010, Christie cancelled the Access to the Region's Core project, which would have constructed two new tunnels under the Hudson River and a new terminal station in New York City for NJ Transit commuter trains. He cited escalating costs and possible further overruns as the reason for his decision. Proponents of the project said it would have created 6,000 construction jobs per year and 45,000 secondary jobs once complete. After the cancellation, New Jersey had to return $95 million to the federal government, and used $1.8 billion of Port Authority of New York and New Jersey money from the project budget to pay for repairs to the Pulaski Skyway, since the New Jersey Transportation Trust Fund that should fund such maintenance is effectively bankrupt. The termination of the project has made the need for increased rail capacity under the Hudson River more urgent, and Amtrak's Gateway Project to bore new tunnels is currently unfunded.

In October 2011, Christie said that he had in fact reconsidered his decision but had again decided not to run for President, stating at a press conference: "New Jersey, whether you like it or not, you're stuck with me." Christie endorsed Mitt Romney for President a few days later.

Political commentators debated whether Christie's weight would or should affect his viability as a 2012 presidential candidate, either for medical or social reasons. In 2011, columnist Eugene Robinson applied the term "extremely obese" to Christie, citing medical guidelines established by the National Institutes of Health. Christie himself was reportedly concerned about his weight and its implications for his health, describing himself as relatively healthy overall.

In the aftermath of the election, Christie maintained his national profile and continued to clash with conservatives in his party by strongly criticizing House Speaker John Boehner regarding aid for Hurricane Sandy and then the National Rifle Association for their ad that mentioned President Obama's children. Christie was subsequently not invited to speak at the 2013 Conservative Political Action Conference (CPAC), which is largely seen as a stepping-stone for Republicans running for President. The CPAC chair explained that Christie was not invited "for decisions that he made", but that "hopefully next year he's back on the right track and being a conservative."

Christie presided over net gains in Republican governorships in the 2014 elections, including for Republican gubernatorial candidates in three largely Democratic states: Bruce Rauner in Illinois, Larry Hogan in Maryland and Charlie Baker in Massachusetts.

In January 2015, Christie took his first formal step towards a presidential candidacy by forming a political action committee (PAC) in order to raise funds and prepare for a likely 2016 presidential bid. On June 27, 2015, Christie launched his presidential campaign website. He formally announced his candidacy on June 30, 2015.

In September 2016, Christie acknowledged that the Fort Lee lane closure scandal, also known as Bridgegate, was a factor in his being denied the nomination. Trump had said earlier that Christie knew about the closures, which Christie denies. Following the release of Trump's tape-recorded comments on an Access Hollywood bus, Christie called Trump's comments "completely indefensible", but also added "I don't think it’s the only way you should make a judgment."

In March 2017, Trump picked Christie to chair the President's Commission on Combating Drug Addiction and Opioid Crisis, an advisory committee on the opioid epidemic.

In January 2018, Christie joined ABC News as a regular network contributor.