[1] In 1868, McCrary successfully sought a U.S. House seat from Iowa's 1st congressional district to succeed Radical Republican James F. Wilson.

[8] He helped create the Electoral Commission to resolve the outcome of the 1876 Presidential Election, and served on the committee that investigated the Crédit Mobilier scandal.

During his House years, McCrary allied with the congressional "Half-Breeds,"[10] the loosely organized and more moderate wing of the Republican Party (in comparison to the pro-spoils system Stalwarts) which emphasized industrial interests and protective tariffs in addition to supporting civil service reform.

McCrary was the 33rd United States Secretary of War in the cabinet of President Rutherford B. Hayes from March 12, 1877, to December 11, 1879, when he resigned.

McCrary was elected as a 3rd Class (honorary) member of the Military Order of the Loyal Legion of the United States (MOLLUS).

[1] He served as general counsel for the Atchison, Topeka and Santa Fe Railroad Company in Kansas City, Missouri from 1884 to 1890.