In 1999, Providence District Supervisor Gerry Connolly appointed Smyth to the Fairfax County Planning Commission to replace attorney Carl A. S. Coan, Jr.[1] When Connolly decided to run for Chairman of the Board of Supervisors following Katherine Hanley's decision to not seek a second term in 2003, Smyth decided to seek the Providence District seat he would be vacating.
[2][3] At the Democratic caucus held in May 2003, Smyth, backed by Connolly, defeated slow growth advocate Becky Cate, who was supported by former Board Chairman Audrey Moore, and Pat Morrison.
[4] She was elected to her first term as Supervisor for the Providence District in November 2003, defeating Republican James E. Hyland, and sworn in on December 15, 2003.
[5][6] Unhappiness with development projects in Smyth's Providence District, such as in Tysons Corner and the Merrifield-Dunn Loring neighborhood, as well as the development of the MetroWest planned community near the Vienna Metro station, led to community activist Charles W. Hall challenging Smyth in the 2007 Democratic primary.
In addition, Smyth is the on the Board of Directors of the Virginia Association of Counties and serves on the Metropolitan Washington Council of Governments Transportation Planning Board and Metropolitan Washington Air Quality Committee, and the Northern Virginia Regional Commission.