FCD adds the six-foot-three winger, who turned pro in 2012 after two seasons at the University of Virginia.
Span, 21, spent the past two seasons with Swedish first-division side Djurgardens IF after MLS did not offer him a Generation Adidas contract following his sophomore season at the University of Virginia. In Sweden, Span made 14 appearances and scored one goal before his contract was not renewed following the 2013 season.
Prior to moving abroad, Span played two years at the University of Virginia, where he scored 12 goals and added eight assists.
FC Dallas was the favorite to land Span going into Thursday’s draft with a 41.1 percent chance. The Chicago Fire (27 percent), San Jose Earthquakes (18.7 percent), New England Revolution (12.3 percent) and Real Salt Lake (0.9 percent) were also in the lottery.