Jeff Smith, a St. Louis Democrat, told U.S. District Judge Carol Jackson he blamed himself for his downfall. He said he sought "any advantage" to win a race for Congress in 2004.
Smith resigned from the state legislature in August after he pleaded guilty to obstruction of justice.
"I was raised better than that, but I thought the ends justified the means," Smith said. "I squandered my reputation and my political career. I squandered what I loved the most."
Former state Rep. Peter Brown, who helped Smith with his 2004 campaign, and Nick Adams, another campaign worker, were sentenced to probation.
The alleged obstruction involved an anonymous mailing that attacked Democratic state Rep. Russ Carnahan, Smith's primary opponent. Carnahan went on to succeed Rep. Dick Gephardt, D-Mo., in Congress.
Florida bear attack: Black bear mauls woman's face
Toddler uninjured after being knocked over by Obama family dog