Born in a displaced persons camp in Eschwege, Allied-occupied Germany, Gejdenson was the child of a Belarusian father and Lithuanian mother. Gejdenson grew up on a dairy farm in Bozrah, near Norwich. He attended Mitchell College for two years and finished his studies at the University of Connecticut. From 1970 to 1973, he worked for the FIA Company. He was elected as a Democrat to the Connecticut House of Representatives that same year and served two terms. He then worked as the president of the Montessori School in Norwich, Connecticut. Gejdenson won a seat in the United States House of Representatives in November 1980. During his tenure, there was strong disagreement whether or not Gejdenson was a strong advocate for the submarine manufacturing base located in his congressional district. Twice Gejdenson was offered a seat on the Armed Services Committee, but declined it. Gejdenson's supporters claimed the congressman didn't need to be on the committee to be effective. Gejdenson served as Chairman of the Subcommittee on Oversight and Investigationsof the House Interior Committee. In that capacity, he conducted oversight over the Nuclear Regulatory Commission and the Bureau of Indian Affairs. Beginning in 1989, Gejdenson assumed the Chairmanship of the Subcommittee on International Economic Policy and Trade of the House Foreign Affairs Committee. Gejdenson focused his subcommittee's work on promoting American exports and streamlining export controls to facilitate high-tech exports. In 1999, Gejdenson became the Ranking Democratic Member of the full International Relations Committee, where he was a key player in writing legislation cracking down on international human trafficking and to authorize the activities of State Department. During his tenure, Gejdenson had a number of very close campaigns for re-election. He was nearly defeated by Republican Roberta Koontz in 1984 and again by State Senator Edward W. Munster in 1992. In 1994, as the Democrats lost control of the House of Representatives, a Gejdenson-Munster rematch produced only a 21-vote victory for Gejdenson. Munster formally challenged the result, which were upheld by the Republican-controlled House Government Reform and Oversight Committee by a vote of 2-1.
Defeat
In November 2000, Gejdenson lost his bid for re-election to the 107th Congress to State Representative Rob Simmons. Three major issues may have caused this defeat. In 1998, he had prominently written a counter-letter urging President Clinton to continue his peacemaking. The American Israel Public Affairs Committee, which had circulated a letter among Congressman to oppose putting any pressure on Israel, opposed his re-election despite the fact that he was Jewish. It was alleged that Gejdenson had moved out of the district. It was also alleged by author Jeffrey Benedict that Gejdenson had been an advocate of letting the Pequot Indians build the Foxwoods Casino.