After serving in the United States Army Air Forces during World War II, Clark won election as city controller in 1949.
[3] His mother, whose family owned Avery Island in Louisiana, was the niece of Edmund McIlhenny, the inventor of Tabasco sauce.
[6] He was elected to Phi Beta Kappa and graduated magna cum laude in 1923 with a Bachelor of Science degree in government, history and economics.
[2] During the 1928 election, Clark founded the Democratic Warriors Club with Richardson Dilworth, beginning a long political partnership between the two.
[4] Both men became active in the reform movement to end corruption in city government, which was long controlled by a Republican machine.
[4] Clark was an unsuccessful candidate for the Philadelphia City Council in 1933, with Dilworth serving as his campaign manager.
[8] Following the entry of the United States into World War II, he was transferred to the China Burma India Theater as deputy chief of staff to General George E.
[2] He briefly served as acting chief of staff to General Stratemeyer, and attained the rank of colonel on October 15, 1943.
[8] Returning to the United States in September 1945, he accompanied General Stratemeyer to Washington, D.C., where he helped design plans to defend the nation against air raids.
[8] Serving from 1950 to 1952, Clark investigated and publicized scandals within the Republican-controlled city government, including the embezzlement of tax money and court funds, imprisonment of the fire marshal, falsification of records, and corruption in the water bureau.
[10] Running on his record as city controller, Clark often used a broom while campaigning as a symbol of his pledge to "sweep out" corruption.
A 1993 survey of historians, political scientists and urban experts conducted by Melvin G. Holli of the University of Illinois at Chicago ranked Clark as the twenty-second-best American big-city mayor to have served between the years 1820 and 1993.
[4] After winning the Democratic nomination over the opposition of Philadelphia's party leaders, he faced first-term Republican incumbent James H. Duff, a popular former governor, in the general election.
[14] During the campaign, Clark ran on a liberal platform which included support for increasing the minimum wage, expanding Social Security, and repealing the Taft–Hartley Act.
[15] He also criticized President Dwight D. Eisenhower on international and domestic matters, and attacked Senator Duff's poor attendance record.
[15] During his early tenure in the Senate, Clark earned a reputation as a strong supporter of civil rights and congressional reform.
[8] In 1962, Clark was re-elected to a second term after narrowly defeating Congressman James E. Van Zandt by a 51%-49% margin.
[11] In 1964, he endorsed Genevieve Blatt, the state Secretary of Internal Affairs, over Judge Michael Musmanno in the Democratic senatorial primary.
[7] He also served as chairman of the Coalition on National Priorities and Military Policy, and continued to attend meetings of Members of Congress for Peace Through Law.
[11] A strong opponent of Mayor Frank Rizzo, he supported Bill Green III in the 1971 Democratic primary and then Republican W. Thacher Longstreth in the general election.
[23] Percy's daughter Mary was married to Nelson Rockefeller from 1930 to 1962, before he served as Vice President of the United States.
[citation needed] Clark's paternal grandmother was the daughter of Joseph and Jane (née Todhunter) Sill, who were social reformers and leaders in antebellum Philadelphia's benevolence movement.