Long considered one of the most innovative visual effects directors in the industry, William Mesa made his name as Vice-President of Introvision. While at Introvision, he was the supervisor/director of visual effects for such diverse films as Rob Reiner's Stand By Me, Stallone's Rambo 3 (1988); Sam Raimi's Karanlık Adam (1990) and Karanlığın Ordusu (1992); Andy Davis' Kuşatma Altında (1992); Bruce Beresford's Bayan Daisy ve Şoförü (1989), and Peter Weir's Korkusuz (1993).

William directed the effects work on Andy Davis's Mega-hit Kaçak (1993). He was instrumental in the now-legendary train crash with Harrison Ford.

William has been the recipient of many awards over the years. In 1988, William received the Technical Achievement Award from the Academy of Motion Picture Arts & Sciences. In 1993, he received a British Academy Award Nomination for Best Visual Effects on the Fugitive. He has won three Emmy Awards for his visual effects on the CBS telefilm, Miracle Landing (1990), the Hallmark Hall of Fame special, The Hugga Bunch (1985) and most recently for the HBO mini-series The Pacific. He also received numerous other awards. In 2001, won seven major awards for Best Commercial Visual Effects for the Batman/Onstar commercials and he won Visual Effects Society Awards for Son Samuray (2003) and The Pacific (2010).

In 1993 William founded Flash Film Works Inc. Under this company William directed the science fiction action adventure Terminal Force a.k.a. Galaxis (1995) for HBO as well as the CD ROM game Maximum Surge (1996). His second directorial was the picture _DNA (1997/I)_, that premiered on HBO. William Mesa continues to visual effects supervise such works as _Wes Craven's New Nightmare_, Sucu (1998), Ölümüne Takip (2002), Kuyu (2003) and Koruyucu (2006). Flash Film Works has also worked on such films as Mavi Korku (1999), Kırmızı gezegen (2000), Pluto Nash'in Maceraları (2002), Son Samuray (2003) and Dostluğun Gücü (2011).

William also co-produced the web series Dragon Age: Redemption.