Cropp started her first term representing Ward 4 on the D.C. Board of Education in 1980.[12] She was elected vice president of the Board of Education in December 1984,[13] and then president in January 1989.[7]
In 1988, Cropp ran to represent Ward 4 on the Council of the District of Columbia.[14] She criticized incumbent Charlene Drew Jarvis, saying Jarvis had too much allegiance to big businesses because they were the source of the great majority of her campaign contributions.[15] Cropp also said that Jarvis had not done enough to help small businesses along Georgia Avenue.[15] Jarvis criticized Cropp for the disappointing results of public schools under Cropp's leadership of the Board of Education.[15] The editorial board of The Washington Post endorsed Jarvis' reelection.[16] Cropp was defeated by Jarvis in the Democratic Party primary election, 47% to 52%.[17]
When Council Member Betty Ann Kane decided not to run for reelection to her at-large seat in 1990,[18] Cropp ran to replace her.[19] The editorial board of the Washington Post endorsed the campaign of her opponent, Johnny Barnes.[20] Cropp won the Democratic Party primary election, receiving 51 percent of the vote; Johnny Barnes received 27 percent, and Terry Lynch received 22 percent.[21] Cropp went on to win the general election with 38 percent of the vote.[22]
1992 elected as chair of the Councilors Committee on Human Services[12]
1994 re-elected at-large member of D.C. Council
1997 named acting Chairman of D.C. Council, following the death of David Clarke
1997 elected D.C. Council Chairman in a special election
1998 re-elected D.C. Council Chairman
2002 re-elected D.C. Council Chairman
2006 entered race for Mayor
After her 2006 loss, Cropp retired from politics. Cropp joined the board of two not-for-profit companies, the Community Preservation and Development Corp. and CareFirst BlueCross BlueShield, and also volunteered for two other local charities, Capital City Links and the D.C. chapter of Boys Town.[23] In 2013, CareFirst BlueCross BlueShield promoted her to chairman of the board.[24]