Walter Duncan McIndoe (March 30, 1819August 22, 1872) was a Scottish American immigrant, lumber industrialist, Republican politician, and Wisconsin pioneer. He served two terms in the U.S. House of Representatives, representing Wisconsin's 6th congressional district for the 38th and 39th congresses (1863–1867). He previously served three terms in the Wisconsin State Assembly (1850, 1854, 1855), representing Portage County.
Born in Dunbartonshire, Scotland, McIndoe immigrated to the United States in 1834. He engaged in business in New York, Charleston, and St. Louis, finally settling in the Wisconsin Territory in 1845 where he became involved in the lumber business.
He served as a member of the Wisconsin State Assembly in 1850, 1854, and 1855. In 1850 as a member of the Assembly he introduced a bill changing the name of his home community from "Big Bull Falls" to Wausau and creating Marathon County. Initially a Whig, in 1854 he became a member of the newly formed Republican Party.
He was a candidate for the Republican nomination for Governor of Wisconsin at the 1857 Republican state convention, contending with Edward Dwight Holton, with both candidates losing to the eventual nominee and governor, Alexander Randall.
During the American Civil War he was provost marshal of Wisconsin.
McIndoe was first elected to Congress in the December 1862 special election to replace Congressman Luther Hanchett, who died three weeks after the 1862 general election. Hanchett was the incumbent in Wisconsin's 2nd congressional district and, in the 1862 general election, had been elected to Wisconsin's newly-created 6th congressional district. McIndoe's election allowed him to replace Hanchett for the last months of the 37th Congress and also for the full term of the 38th Congress. He was subsequently re-elected in 1864 to the 39th Congress, ultimately serving from January 26, 1863, until March 3, 1867.
During the Thirty-ninth Congress, he served as chairman of the House Committee on Revolutionary Pensions.
In 1866, McIndoe declined candidacy for renomination, instead resuming his interests in the lumber business.
He died in Wausau, Wisconsin, on August 22, 1872, and was interred at Pine Grove Cemetery.
| colspan="6" style="text-align:center;background-color: #e9e9e9;"| Special Election, December 30, 1862
| colspan="6" style="text-align:center;background-color: #e9e9e9;"| General Election, November 8, 1864