Orr entered politics as an "independent Democrat", opposed to the official Democratic Party organization. The party organization was then controlled by the "Machine" created by Mayor Richard J. Daley, who died in December 1976. In February 1979, Orr was elected alderman from the 49th Ward, which covered most of the Rogers Park neighborhood in the far northeastern corner of Chicago. Orr joined with other white "independent" aldermen from the "Lakefront" and black dissident aldermen from the south side and west side in opposing the corruption and racism of the Machine. Orr was re-elected in February 1983 and 1987. In February 1983, with the Machine divided between supporters of Jane Byrne and Richard M. Daley, black independent Harold Washington became Mayor. Washington was opposed by 29 aldermen who tried to paralyze city government for three years in what was dubbed "Council Wars." Orr backed Washington, one of only five white aldermen to do so. After the Washington coalition won the majority in 1986, after special aldermanic elections were held, Orr was elected by the City Council in 1987 to serve as the city's Vice Mayor. In 1986, Orr, with the assistance of fellow alderman Bernard Stone, successfully pushed an ordinance through City Council that declared Chicago a "nuclear-free zone". In May 1988, the City Council voted to oust Orr from his position as Vice Mayor as retribution for his attempts to make reforms that would have held the council's committees more accountable for the budgets they manage. When Orr was elected County Clerk in 1990, then-mayor Richard M. Daley appointed Robert Clarke as his replacement. In the 1991 aldermanic election, Clarke was defeated by Joe Moore, whom Orr had endorsed.
When Mayor Washington died of a heart attack on November 25, 1987, Orr, as Vice Mayor, became actor mayor. He took office on November 25 and served for a week until the Council elected a permanent replacement mayor. Orr was suggested as the obvious choice, but as a reformer, he was vehemently opposed by the remaining Machine aldermen, and many black Chicagoans wanted a black replacement for Washington. Alderman Eugene Sawyer, who was black, and before 1983 had been a Machine loyalist, was chosen instead on December 2, 1987. Orr chaired Council meetings as mayor on December 1, a memorial meeting for Washington, and on December 2, when Sawyer was selected as his replacement.
County Clerk (1990-2018)
In 1990, the office of County Clerk was vacated by Stanley T. Kusper, Jr. who ran unsuccessfully for Cook County Board President. Orr ran for the office, and won the Democratic primary handily with 56% of the vote against two opponents. He also won easily in the general election, receiving more votes than any other candidate for county office. He was re-elected in 1994, 1998, 2002, 2006, 2010, and 2014. In 1998, 2002, 2006, and 2010, he was unopposed for renomination, and faced only token opposition in the general election. On June 21, 2017, he announced that he would not run for reelection to an eighth term. Karen Yarbrough, the then-Cook County Recorder of Deeds, succeeded Orr as the Clerk.