He is of mostly English, with some German, Irish, and Welsh, ancestry. His paternal grandfather and great-grandfather were born in Canada, but many of Grant's family lines have been in the United States since the 1600s.
In an interview with Entertainment Weekly, Gustin stated that he has a Superman tattoo.
Wrongly tweeted his phone number in October 2011 in grantgust twitter and caused 20 fans call him in 10 minutes. Changed phone number in 5 minutes through AT&T.
In a relationship with Hannah Douglass since 2014.
He has played the same character (Barry Allen / The Flash) in five different television series: Arrow (2012), The Flash (2014), Vixen (2015), Supergirl (2015) and DC's Legends of Tomorrow (2016).
He is married to LA Thoma since December 15th 2018.
He and his The Flash (2014) co-star John Wesley Shipp, who played Barry Allen in The Flash (1990), were both born in Norfolk, Virginia.