He graduated with aBachelor of Science in chemistry fromGurukul Kangri University in Haridwar.[14] Following this, he worked as a chemist inVadodara for a year, before leaving forDelhi in search of a new job. Once in Delhi, he was instantly drawn to acting after watching a play. In pursuit of securing admission to theNational School of Drama (NSD) inNew Delhi,[14] he acted in over ten plays with a group of friends, including one inDehradun,[12] to fulfill one of the criteria for admission.[3]
He made hisBollywood debut in the year 1999 with a small role in theAamir Khan starrerSarfarosh.[17] He then appeared inRam Gopal Varma's 1999 filmShool and the 2000 filmJungle, as well asRajkumar Hirani'sMunnabhai MBBS (2003). After moving to Mumbai, he tried to get work in television serials but did not achieve much success.[18][19] He did a short film,The Bypass, in 2003, where he appeared withIrrfan Khan.[20] Beyond that, between 2002 and 2005, he was largely out of work and lived in a flat that he shared with four other people, surviving by conducting occasional acting workshops.[18] In 2004, which was one of the worst years of his struggle, Siddiqui couldn't pay rent. He asked an NSD senior if he could stay with him. The senior allowed him to share his apartment inGoregaon suburb if he was willing to cook meals for him.[21]
Between 2004 and 2007, Siddiqui had a few minor roles, including in the filmBlack Friday, which came out in 2007 and was a nominee for theGolden Leopard. In 2009, he appeared in a cameo role in the song "Emotional Atyachar" in the movieDev D, playing the role of Rangila. He performed a duet with Rasila (known together as Patna ke Presley). In the same year, he appeared inNew York. However, it was his role of a journalist inAnusha Rizvi's 2010 filmPeepli Live, that first got him wide recognition as an actor.[22] In 2012, he appeared inPrashant Bhargava'sPatang: The Kite, which premiered at theBerlin International Film Festival and theTribeca Film Festival. Siddiqui's performance was praised by film criticRoger Ebert,[23] who stated that the role "transformed his acting style"[24] and he awarded the actor the 'Thumbsup Trophy'. The film was subsequently released in the U.S. and Canada and garnered much attention, with rave reviews fromThe New York Times.[25]
In 2015, Siddiqui's filmsBajrangi Bhaijaan andManjhi – The Mountain Man were released, and he was praised for his roles. His work inRaman Raghav 2.0 in 2016 won him the Fancine Malaga Award in Spain[35] and in theAsia Pacific Screen Awards,[36] both in the category of Best Actor. The 2018 filmManto, based on the life of Urdu authorSaadat Hasan Manto, won him Best Actor at the 2018 Asia Pacific Screen Awards.[7]
Siddiqui has been married twice. In his youth, he dated a woman named Anjali, who grew up in the same village as he; the couple broke up in 2009.[47] In 2010 or 2011, he married a woman named Sheeba.[47] By 2012, he was dating an American woman named Suzanne.[47] He also had a brief relationship withNiharika Singh, a former Miss India, with whom he co-starred in two films.[47]
Siddiqui eventually reconnected with Anjali, and the couple married and had two children, a daughter and a son. At this point, Anjali took the name Aaliya Siddiqui.[48] In May 2020, Aaliya announced on social media that she was seeking a divorce from Nawazuddin.[49][50]
Siddiqui lives in Mumbai with his younger brother, Shamas Nawab,[51] a film director. When not busy acting, he likes to spend time in his hometown of Budhana, where he owns a farm.[52] In a May 2021 interview, he said that he spends most of his time there.[53]
Siddiqui's first lead role in a feature film was inPrashant Bhargava'sPatang, which premiered at theBerlin Film Festival, in which his performance has been praised by film criticRoger Ebert (awarding the film 4/4 stars),[23] who stated that the role "transformed his acting style".[24]