Benson grew up in New York City. He attended Deerfield Academy and graduated from Columbia University in 2001 with a degree in film and English. Benson was in a long-term relationship with Jessica Chastain. The two lived together before breaking up in 2010.

Benson began his film career writing, directing and acting in shorts. After the premiere of the short film Four Lean Hounds at the Malibu Film Festival, he met Jessica Chastain, who asked him to work on future projects. Together, they worked on their 2010 short film The Westerner. Benson directed their feature film The Disappearance of Eleanor Rigby. After Chastain asked questions about Rigby’s background, Benson wrote another script devoted entirely to her perspective. In 2012, Chastain was officially cast for the film. It was shot as two films simultaneously. Both films premiered together at the 2013 Toronto International Film Festival under the title The Disappearance of Eleanor Rigby: Him and Her Benson later edited the films into one film The Disappearance of Eleanor Rigby: Them which premiered at the 2014 Cannes Film Festival. It was given a limited release in September 2014 by The Weinstein Company. On January 16, 2019, Benson was confirmed as screenwriter for the upcoming Marvel Studios film Black Widow, assuming the position of Jac Schaeffer. He was later replaced in the role by Eric Pearson.