Born in Anchorage, he is the son of U.S. Representative Nick Begich, who disappeared and was presumed dead following a 1972 plane crash. He graduated from high school and has taken continuing education classes at University of Alaska Anchorage, but does not have a college degree. At age 26 he was elected to the Anchorage Assembly. After serving as chairman for three years, he left the Assembly in 1998. Begich ran two unsuccessful campaigns for mayor in 1994 and 2000. He was finally elected in 2003, winning a narrow three-way race by 11 votes.
Begich handily won the Democratic nomination in the state's 2008 U.S. Senate election. He faced longtime incumbent Republican Ted Stevens, who was facing ethics and corruption charges during his re-election campaign. Stevens was convicted of felony violations a week before the election, and Begich won by a narrow margin.
A member of the Moderate Dems Working Group, Begich is considered a moderate Democrat. He is pro-choice and supports ANWR drilling, gun rights, and benefits for same-sex couples. He opposes the Patriot Act. Begich has generally supported President Barack Obama's legislative agenda, including the Patient Protection and Affordable Care Act of 2009 and the Don't Ask, Don't Tell Repeal Act of 2010. Begich became the Chairman of the Democratic Steering and Outreach Committee in 2011.