Karben was born in the borough of The Bronx. In 1979, his family moved to Spring Valley, New York. Karben was a student at the Frisch School in Paramus, New Jersey). He attended Yeshiva University as a Max Stern Distinguished Scholar and graduated magna cum laude in 1996 with a B.A. in English. He then attended the Columbia Law School as a Harlan Fiske Stone Scholar, graduating in 1999.
Karben is a member of the American Bar Association and the New York State Bar Association.
Karben married Lauren C. Bekritsky, his high school sweetheart, in June 1996. The Karbens have three daughters.
In 1995, Karben lost his initial bid to become county legislator at the age of 21 when he finished 4th in a race for three open positions. In his concession speech at the Holiday Inn in Suffern, New York, Karben assured his supporters that he considered the election a positive experience and that he would be back.
In 1997, Karben was elected to represent Ramapo in the Rockland County Legislature. He was the youngest county lawmaker in the State of New York at that time and remains the youngest person to have served in the Rockland County Legislature. Karben was selected as majority leader of the Rockland County Legislature in 2001 - 2002.
In November 2002, Karben was elected to the New York State Assembly in Albany to represent the 95th district, which includes the Town of Orangetown and parts of the Town of Ramapo in Rockland County. Karben served on the Energy Committee and led an investigation of Consolidated Edison in 2004. Karben had also pushed for tougher sex-offender tracking laws and environmental cleanups at several Rockland County sites.
On May 18, 2006, Karben unexpectedly announced his resignation from the New York Assembly. It was reported that Karben had been the subject of an internal legislative investigation into alleged sexual advances toward male staffers. Among the allegations probed by the lower chamber was that Karben had recently viewed a pornographic video with three male interns at an Albany apartment. A male Assembly staffer in his 20s, who spoke on condition of anonymity, said Karben made what he took as a pass at him recently inside the Legislative Office Building. "It really made me uncomfortable," he said. No formal complaints against Karben were ever filed.
Subsequently, Karben left his position as a partner in the Spring Valley law firm of Kurtzman, Matera, Scuderi, Gurock, and Karben. The firm has refused to publicly state how they arrived at the decision for Karben to leave
Karben had also been involved in a fundraising controversy involving Charles Kushner, a New Jersey developer who served a prison sentence for hiring prostitutes in an attempt to influence potential witnesses in a New Jersey investigation. Kushner had contributed over $40,000 to Karben's campaign, and Karben contributed $2,500 to charity after revelations about Kushner surfaced.
Following his resignation, he started his own law firm, the Law Office of Ryan Karben, based at his home in Monsey. In September 2007, Karben was named Managing Director of Fleishman-Hillard Government Relations, a national political consulting and lobbying firm.