He graduated with a Bachelor of Science in chemistry from Gurukul Kangri University in Haridwar.[13] Following this, he worked as a chemist in Vadodara for a year, before leaving for Delhi 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 the National School of Drama (NSD) in New Delhi,[13] he acted in over ten plays with a group of friends, including one in Dehradun,[11] to fulfill one of the criteria for admission.[3]
He made his Bollywood debut in the year 1999 with a small role in the Aamir Khan starrer Sarfarosh.[19] He then appeared in Ram Gopal Varma's 1999 film Shool and the 2000 film Jungle, as well as Rajkumar Hirani's Munnabhai MBBS (2003). After moving to Mumbai, he tried to get work in television serials but did not achieve much success.[20][21] He did a short film, The Bypass, in 2003, where he appeared with Irrfan Khan.[22] 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.[20] 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 in Goregaon suburb if he was willing to cook meals for him.[23]
Between 2004 and 2007, Siddiqui had a few minor roles, including in the film Black Friday, which came out in 2007 and was a nominee for the Golden Leopard. In 2009, he appeared in a cameo role in the song "Emotional Atyachar" in the movie Dev D, playing the role of Rangila. He performed a duet with Rasila (known together as Patna ke Presley). In the same year, he appeared in New York. However, it was his role of a journalist in Anusha Rizvi's 2010 film Peepli Live, that first got him wide recognition as an actor.[24] In 2012, he appeared in Prashant Bhargava's Patang: The Kite, which premiered at the Berlin International Film Festival and the Tribeca Film Festival. Siddiqui's performance was praised by film critic Roger Ebert,[25] who stated that the role "transformed his acting style"[26] 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 from The New York Times.[27]
In 2015, Siddiqui's films Bajrangi Bhaijaan and Manjhi – The Mountain Man were released, and he was praised for his roles. His work in Raman Raghav 2.0 in 2016 won him the Fancine Malaga Award in Spain[5] and in the Asia Pacific Screen Awards,[37] both in the category of Best Actor. The 2018 film Manto was a groundbreaking performance that won him Best Actor at the 2018 Asia Pacific Screen Awards.[6]
Celebrated author Paulo Coelho has recommended Sacred Games to his Twitter followers and lauded Nawazuddin's work, calling it "One of the best series on Netflix with the great actor Nawazuddin".[38]
In 2021, he was seen in the American-Bangladeshi-Indian film No Land's Man.[39]
Siddiqui has been married twice. He was in a relationship with a woman named Anjana Kishor Pandey, which ended in 2007.[citation needed] Siddiqui then married a woman named Sheeba, a marriage that did not last long, and the couple divorced in 2010. By this time, Siddiqui was dating a woman from New Jersey named Suzanne, and he also had a brief relationship with Niharika Singh, a former Miss India, with whom he co-starred in two films.[43]
Siddiqui later reconnected with Pandey, and after she converted to Islam and changed her first name to Aalia, they married and had two children, a daughter and a son.[44] The marriage soon went downhill, however, and in May 2020, Aalia Siddiqui announced on social media that she was seeking a divorce.[45][46]
Siddiqui lives in Mumbai with his younger brother, Shamas Nawab,[47] an aspiring film director. When not busy acting, he likes to spend time in his hometown of Budhana, where he owns a farm.[48] In a May 2021 interview, he revealed that he now spends the major part of his time there.[49]
Siddiqui's first lead role in a feature film was in Prashant Bhargava's Patang, which premiered at the Berlin Film Festival, in which his performance has been praised by noted film critic Roger Ebert (awarding the film 4/4 stars),[25] who stated that the role "transformed his acting style".[26]