In 1983, Marshall was hired by the leading Texas firm Haag Engineering and eventually became Senior Engineer and Meteorologist. At Haag, he travels a great deal surveying storm damage across the United States. He has conducted more than 10,000 damage surveys of hailstorms, tornadoes, and hurricanes. Some of the famous tornadoes he surveyed include the F5s at Jarrell, Texas (1997), Bridge Creek, Oklahoma (1999), Greensburg, Kansas (2007), Alabama (2011), Joplin, Missouri (2011), and Moore, Oklahoma (2013). Some of the famous hurricanes he has surveyed include Alicia in Texas (1983), Hugo in South Carolina (1989), Andrew in Florida (1992), Opal in Florida (1995), Katrina in Mississippi (2005), and Ike in Texas (2008). He became a Professional Engineer in 1989.