Gov. David Paterson appointed the second-term congresswoman from upstate New York on Friday. She was named to the post after Caroline Kennedy, the presumed front-runner, withdrew from contention because of personal reasons.
Gillibrand fills a seat vacated when Sen. Hillary Rodham Clinton became secretary of state.
At age 42, Gillibrand is the youngest U.S. senator. She is the 17th woman to serve in the Senate.