Leach was the John L. Weinberg Visiting Professor of Public and International Affairs at the Woodrow Wilson School of Princeton University.

in politics after completing a senior thesis titled "The Right to Revolt: John Locke Contrasted with Karl Marx.

[13] In 1973, Leach resigned his commission in protest of the Saturday Night Massacre when Richard Nixon fired his Attorney General, Elliot Richardson, and the independent counsel investigating the Watergate break-in, Archibald Cox.

[14] After returning to Iowa to head a family business, Leach was elected in 1976 to Congress (defeating two-term Democrat Edward Mezvinsky), where he came to be a leader of a small band of moderate Republicans.

[18] During his 15 terms in Congress, Leach's voting record was generally conservative on fiscal issues, moderate on social matters, and progressive in foreign policy.

As chair of the Arms Control and Foreign Policy Caucus, he pressed for a Comprehensive Test Ban and led the first House debate on a nuclear freeze.

He pushed for full funding of U.S. obligations to the United Nations, supported U.S. re-entry into UNESCO, and opposed U.S. withdrawal from the compulsory jurisdiction of the International Court of Justice.

[21][22] He was one of three Republican congressmen (alongside Michael Castle and Amo Houghton) to vote against the 2003 extension of the Bush-era tax cuts.

[27] As a member of the minority for his first nine terms, he became known for the development of three reports – one in the 1980s calling for a more progressive approach to Central American politics; a second in the early 1990s on reforming the United Nations written for a national commission he legislatively established and later chaired; and the third issued when he was ranking minority member of the Banking Committee on the challenges of regulating derivatives.

[30] Leach was a top critic of President Bill Clinton and played a leading role in the House's investigation of the Whitewater scandal.

[citation needed] In the end, the independent counsel brought more than 50 criminal convictions related to the failed S&L, including cases against Clinton's successor as Governor of Arkansas, Jim Guy Tucker, and his business partners in Whitewater.

[citation needed] Leach seriously considered running against fellow Republican incumbent Jim Nussle in the 1st District primary.

[citation needed] In 2006, Leach was defeated in a considerable upset by Democratic opponent Dave Loebsack, a political science professor at Cornell College.

The bill had been subject to extensive hearings over several Congresses, especially on the House side where both the Financial Services and the Judiciary committees had shared jurisdiction.

[60] Leach resided in Iowa City and Princeton with his wife Elisabeth (Deba), son Gallagher, and daughter Jenny.

[61] On August 12, 2008, Leach broke party ranks to endorse Democrat Barack Obama over fellow Republican John McCain in the 2008 U.S. presidential election.

[1] On August 1, 2013, Jim Leach began serving a three-year term as public affairs chair at the University of Iowa and he was slated to begin teaching there as a visiting professor of law in the spring of 2014.

"[68] In 2022, Leach revealed in an interview with the Quad-City Times that he had changed his registration to Democratic ahead of the June primary, citing his switch as a rebuke of the national party and their response to the January 6 United States Capitol attack the previous year.