- He was born into a Zamindar Muslim Family called as Numberdars.
- He has a degree in Chemistry, and during his days of struggle, he worked at a Chemist shop in Vadodara.
- He moved to Delhi to pursue his acting aspirations and joined a theatre group. Since there was not enough money in theatres, he worked as a watchman for the subsistence for around 5 years.
- He made his Bollywood debut in 1999 with a very small role in the Aamir Khan starrer film- Sarfarosh.
- He appeared as a pickpocket in the 2003 comedy-drama- Munna Bhai M.B.B.S.- starring Sunil Dutt and Sanjay Dutt.
- His first lead role appearance in a feature film was as a wedding singer- Chakku in Prashant Bhargava’s Patang (2007-08). Nawazuddin considers his role in the film as the turning point of her acting career.
- He also appeared in a cameo role in the song- Emotional Atyachar of the 2009 movie- Dev D.
- He has worked with all the 3 Khans of Bollywood. (Salman Khan– Bajrangi Bhaijaan, Aamir Khan– Talaash & Shah Rukh Khan– Raees).
- He appeared in the 2012 version of Aamir Khan Talash.
Siddiqui went to the National School of Drama, New Delhi. After graduating from NSD in 1996, he moved to Mumbai.
Siddiqui made his debut at Bollywood in 1999, with a small role in Sarfarosh of the Aamir Khan. He later appeared in Shool by Ram Gopal Varma (1999), Jungle (2000); and Munnabhai MBBS by Rajkumar Hirani (2003). After moving to Mumbai, he tried to get work in TV series, but did not get much success. He made a short film, The Bypass in 2003, where he appeared with Irrfan Khan. n addition, between 2002 and 2005, he was largely unemployed and lived in an apartment he shared with four other people, and he survived by organizing occasional theater workshops.
In 2004, one of the worst years of his struggle, he could not pay rent. He asked a senior from NSD if he could stay with him. The elder allowed him to share his apartment in Goregaon if he was ready to cook for him.
In 2009, he appeared in a role of cameo in the song "Emotional Atyachar" in the film Dev D in his role of Rangila, with his duet partner Rasila . In the same year, he appeared in New York (2009). However, it was his role as a journalist in Anusha Rizvi's Peepli Live (2010), which first earned him wide recognition as an actor.
In 2012, he appeared in Prashant Bhargava's Patang: The Kite (2012) which was featured at the Berlin International Film Festival and the Tribeca Film Festival, for which Siddiqui was hailed by critic Roger Ebert. acting style. "The film was then released in the United States and Canada, and attracted much attention with the New York Times' glowing reviews.
He then appeared in Kahaani (2012), in which he played the archetype of the angry intelligence agent Khan. The gangster epic of Anurag Kashyap Gangs of Wasseypur followed, which contributed to his fame. He played his first lead role as Sonu Duggal in Ashim Ahluwalia's Miss Lovely, which premiered at the 2012 Cannes Film Festival, a role that Siddiqui describes as his most real performance so far. " Siddiqui then followed the sequel to Gangs of Wasseypur.
In 2013, he starred in the horror film Aatma. In 2014, he played the main antagonist Shiv Gajra, in the blockbuster Kick.