Blackthorne's cinematic career commenced with a pivotal role as Captain Andrew Russell in the critically acclaimed Bollywood film Lagaan: Once Upon a Time in India, which garnered an Oscar nomination in 2001. In preparation for the part, he dedicated six months to mastering the intricacies of the Hindi language.
His subsequent film credits include the 2003 drama Mindcrime and the award-winning indie feature length film Four Corners of Suburbia, which premiered in 2005. This critically acclaimed film received accolades at both the Crossroads Film Festival, taking home the Best Narrative Feature award in 2006, and the Avignon Film Festival, where it won the Best Composer category in the same year.
Blackthorne's extensive indie filmography also boasts credits in This Is Not an Exit: The Fictional World of Bret Easton Ellis, released in 1999, as well as a starring role in the British film The Truth Game, which premiered in 2001. Additionally, he appeared alongside Michael Rapaport in the 2006 film Special, playing the character Jonas Exiler.
In 2013, Blackthorne made his directorial debut with the documentary film This American Journey, which follows his journey across America with Australian photographer Mister Basquali. The film features candid interviews with everyday Americans, exploring their thoughts on their country and its future. This American Journey received screenings at several prestigious film festivals, including Hollywood, Carmel, Ojai, and Big Bear, before being released through Cinema Libre Studios.