Mechlowicz was born in New York City, the son of Susan (Lehrman), a respiratory therapist, and Morris Mechlowicz. He was raised in a “tight-knit” Jewish family. He grew up in Plano, Texas, where he graduated from Plano Senior High School in 1999, and attended the University of Texas at Austin for one semester. He subsequently moved to Los Angeles, California, where he studied at UCLA and graduated in 2003, with honors, from the Conservatory Acting Program.

In the film, which was a dark teenage drama, Mechlowicz played the oldest of a group of teenagers. The film received a positive critical reception. He received an Independent Spirit Award for his acting in Mean Creek. In 2004, he made a small appearance in the video for Gavin Degraw's hit song "I don't want to be", in which he plays the romantic interest of Shiri Appleby. In 2005, Mechlowicz guest starred in an episode of the television series House M.D.

Mechlowicz also starred, opposite Nick Nolte and Amy Smart, in the drama Peaceful Warrior (based on the book Way of the Peaceful Warrior), in which he plays the lead role of Dan Millman, a rings Gymnast who is an olympic hopeful. The story is based on the life of the book's author. His next film was the thriller Gone, filmed in 2005 and released in 2007 co-starring Amelia Warner. In 2010, Mechlowicz released two films, Waiting for Forever, co-starring Rachel Bilson, Blythe Danner, Richard Jenkins, and Tom Sturridge, and the dark suspense drama Undocumented starring Mechlowicz and Peter Stormare.

On April 1, 2011, Mechlowicz's film Cat Run, opened in theaters. Cat Run starred Mechlowicz, Paz Vega, and Janet McTeer. In March 2012, Scott's most recent film Eden debuted at the South by Southwest Film Festival in Austin, Texas. In Eden, Mechlowicz took another dark turn, as the boyishly charming bait luring young girls into a sex trafficking ring, based on a true story. Eden costars Beau Bridges and Jamie Chung and was directed by Megan Griffiths.