Before running for political office, Jochum served as chair of the Dubuque County Democratic Central Committee in 1982 and floor whip at the Democratic National Convention in 1984. In 1992 she became the first woman elected to the Iowa Legislature from Dubuque County. She ran on a platform of making state government more responsive to its citizens; campaign finance reform; strong support for education and affordable health care; and job creation. In 2008 Jochum served on the Environmental Protection committee, Labor committee, Ways and Means committee and the State Government Committee where she was chair. She also served on the Justice System Appropriations Subcommittee.
Jochum was named the Legislator of the Year from the Mental Health Association in 1994. In 1995, she received the Jamie Barwick Award for Excellence for outstanding contributions to the lives of children with disabilities. Jochum received the 1996 Leadership Award from the Public Policy Institute for outstanding efforts as chairwoman of the Dubuque County Democratic Party.
In 2008 Jochum was elected to the Iowa Senate. In 2012 less than two weeks after winning a second term in the Iowa Senate, Jochum was elected to the Senate presidency.