Dehnert grew up in Illinois and graduated from Illinois Wesleyan University with a degree in musical theater. She received training as a concert pianist as child and also learned to play the French horn, flute, trumpet and harpsichord, but in college she discovered musical theater. In 1994, at the age of 21, Dehnert entered Trinity Repertory Company's conservatory program in Providence, Rhode Island as a student. She performed there as a musician before becoming a musical director, and later was put in charge of a production.
Some of the shows she staged for Trinity Rep were West Side Story, A Moon for the Misbegotten, The Skin of Our Teeth, Peter Pan, Noises Off, Who's Afraid of Virginia Woolf?, My Fair Lady, Othello and Saint Joan. Iris Fanger wrote that "Audiences have applauded [Dehnert's] ingenuity in setting George Bernard Shaw's "St. Joan" in a neighborhood garage and the entire West Side Story in the high school gym, mixing up the Jets and the Sharks to emphasize their commonalities." In 1999, Dehnert became associate artistic director of the company.
In 2003, working for Trinity Rep, Dehnert directed a reimagined production of Annie "that emphasized the poverty of the Great Depression and the callousness of the Hoover administration." Early in its run, the production included a reworked ending in which Annie wakes to find that the positive events that happened to her throughout the show, including being adopted by billionaire Oliver Warbucks, were all part of a dream. Martin Charnin, who wrote the lyrics for Annie, attended a performance and was critical of the production. He told The New York Post that the production was "not true to the spirit of the show" and that "It was a very WPA, Group Theater, Clifford Odets-y kind of thing." He later met with Trinity Rep executives, who agreed to rework the production, including removing the reworked ending. However, Charles Strouse, who wrote the music for Annie, also saw the production and was impressed, which prompted him to approach Dehnert to produce his new musical, You Never Know. The play had its world premiere at Trinity Rep in April 2005.
Terry Teachout, drama critic for The Wall Street Journal, has praised several of Dehnert's productions. He called Dehnert's 2011 production of William Shakespeare's Julius Caesar for the Oregon Shakespeare Festival "the best Julius Caesar I've ever seen, a stark parable of good intentions run amok that has the attention-grabbing power of a hand grenade lobbed into a crowded room." Teachout later named the production the best Shakespeare production of 2011. Teachout praised Dehnert's 2013 Oregon Shakespeare Festival production of My Fair Lady, which was a minimalist reimagining of the musical in the style of Bertolt Brecht. Teachout was initially skeptical of the reimagining but wrote that Dehnert had "successfully wrought a radical transformation on the familiar parable". Teachout also lauded Dehnert's direction of Kate Hamill's adaptation of "Pride and Prejudice" at Hudson Valley Shakespeare Festival in 2017 saying, "Such a show demands worthy staging, and Amanda Dehnert ... delivers the goods with gusto."
- Fanger, Iris. "A director thanks Providence for her rising career". Christian Science Monitor. Retrieved 18 May 2015.
- Hernandez, Ernio (17 November 2004). "Director Amanda Dehnert Fills in for New Public Theatre Head Oskar Eustis at Trinity Rep". Playbill. Retrieved 19 May 2015.
- Riedel, Michael (13 June 2003). "'Annie,' Go Get Your Gun". New York Post. Retrieved 18 May 2015.
- Rodriguez, Bill (9 May 2003). "Dreams fulfilled". The Providence Phoenix. Archived from the original on 2015-05-21. Retrieved 18 May 2015.
- Hernandez, Ernio. "Tomorrow: New Strouse Musical You Never Know Starts World Premiere at Trinity Rep". Playbill. Retrieved 18 May 2015.
- "The 19th Elliot Norton Awards". Elliot Norton Awards. Boston Theater Critics Association. Retrieved 18 May 2015.
- "Amanda Dehnert". Northwestern University School of Communication. Retrieved 18 May 2015.
- Teachout, Terry. "The Glorious Tragedy of Julius Caesar". The Wall Street Journal. Retrieved 18 May 2015.
- Teachout, Terry (23 December 2011). "Revival of the Fittset: Great Shows Roar Back". The Wall Street Journal.
- Teachout, Terry (18 July 2013). "A Smart Little 'Lady'". The Wall Street Journal. Retrieved 18 May 2015.
- Teachout, Terry (7 July 2017). "A Shakespeare Festival for the 21st Century". The Wall Street Journal. Retrieved 7 July 2017.