 Dart began his career as a state prosecutor in Cook County.Afterwards he was an Illinois State Senator, having been appointed in 1991 to fill the vacancy caused by the resignation of Senator Jeremiah E. Joyce (D-Chicago).He was then elected and served state representative as a Democrat for Illinois' 28th House District from January 1993 until January 2003, before becoming chief of staff to Cook County Sheriff Michael F. Sheahan.