Grantley was educated at the Anglican Church Grammar School in Brisbane, where he graduated in 1997. During his school years, he was a rugby union player and a rower. He was also heavily involved in drama and theatre-sports, and won the Headmaster's Prize for Drama in his senior year. He later attended the Queensland University of Technology.
Grantley began his television acting career in 2003, starring in Fat Cow Motel. Over the next two years, he had small guest roles in Marking Time, Small Claims and The Cooks. In the summer of 2005 / 2006, he had a role in the short lived series headLand. In 2006, he had a small role in Foxtel's Supernova series and in 2007, had a 10-episode guest role in Home and Away.
In 2008, Grantley shot to fame in the high rating drama, Underbelly, where he played antagonist and Criminal Carl Williams. With this role he won the 'Most Outstanding Actor' award at the Logies.
He appeared in two short film entries for the 2009 Tropfest Short Film Festival, including Being Carl Williams where Grantley, playing himself, is abducted by two Criminals who mistake him for Carl Williams after his role in Underbelly.
In 2012, Grantley was cast in a new series, House Husbands, playing the character Kane Albert. In 2015, Grantley left the series after its fourth season, however returned in the fifth season finale for a brief appearance.
He was announced in late 2013 that he would be reprising his role of Carl Williams in the sequel/spin-off series Fat Tony & Co. which was not placed under the Underbelly franchise (due to financing reasons) and focused on the rise and fall of Tony Mokbel, who also featured in the original series, played by Robert Mammone.
In 2017 Gyton took on his first TV presenting role as Host of TEN's Pooches at Play, a lifestyle show all about dogs and our relationship with them. In 2018 he is performing in the theatrical production Hand to God and continues his hosting role on Pooches at Play.
