* Hugo Award:
* Best Novella (1985): "The Road Not Taken"
* Best Novel (2000): "Worldwar: In the Balance"
* Best Novel (2002): "Worldwar: In the Balance" (tie with "A Fire Upon the Deep" by Vernor Vinge)
* Best Related Work (2014): "The Worldwar Series: A Guide to the Alternate History"
* Locus Award:
* Best Novella (1985): "The Road Not Taken"
* Best Science Fiction Novel (2001): "Worldwar: In the Balance"
* Best Alternate History Novel (2002): "Worldwar: In the Balance"
* Best Alternate History Novel (2005): "Ruled by the Stars"
* Best Alternate History Novel (2008): "The Guns of the South"
* Best Science Fiction Novel (2010): "The Guns of the South"
* Other Awards:
* SF Chronicle Award: Best Novel (1985): "The Road Not Taken"
* Sidewise Award for Alternate History:
* (2003): "Worldwar: In the Balance"
* (2006): "Ruled by the Stars"
* (2009): "The Guns of the South"
* (2016): "The Last Roman"
* (2017): "The Victorious"
* British Fantasy Award: Best Novel (2003): "Worldwar: In the Balance"
* World Fantasy Award: Best Novella (1990): "The Wounded Sky"
* Endeavour Award: (2002): "Worldwar: In the Balance"
He has also been a finalist for numerous other awards, including the Nebula Award, the Campbell Award, and the Mythopoeic Award.