Before pursuing acting, O'Nell worked at a
Connecticut-based marketing firm Lester Inc. His job took him to
India,
Philippines, the
UK, and
South Africa. After doing community and regional theater in the
U.S. for a while, he appeared in advertisements for
Hyundai,
Lenovo,
Captain Morgan, Roma Switches,
Panasonic,
Finolex,
7 Up and
eSys. He was the brand ambassador for Mouin Glaciere perfumes from 2006 to 2009.
Film and television Hindi-language cinema O'Nell played a small role in the English comedy
Loins of Punjab Presents (2007). His first cinematic release was the dry
Hindi-language comedy
Cheeni Kum (2007) in which he plays a bumbling English waiter with a turbulent relationship with his boss
Amitabh Bachchan. In the same year, O'Nell appeared as a contestant on season three of the Indian celebrity dance competition
Nach Baliye where he was paired with actor
Sweta Keswani. He is the first non-Indian participant on the show by that time. In 2009, O'Nell played
Sweta Keswani's husband in
Rohit Roy's made-for-television film
Chaar Mulakatein. He was next seen in
Malik Ek (2010) featuring
Jackie Shroff,
Smriti Irani, Rajeshwari Sachdeva,
Shakti Kapoor, and
Divya Dutta. O'Nell returned to television for
Zee TV's historical drama
Jhansi Ki Rani, playing Robert Ellis, a British officer sympathetic to the
Rani Laxmi Bai-led 1850s revolutionary struggle against the colonial rule. His character is loosely based on the eponymous historical figure whose relationship with Rani Laxmi Bai is the subject of a fictional book
Rani by Jaishree Misra. The book attracted significant controversy for historical
revisionism, and was subsequently banned in present-day
Jhansi. O'Nell also appeared in a guest role on the
Star One TV's
Dhoondh Legi Manzil Humein as Ralph, the protagonist's abusive boyfriend. O'Nell had a supporting role in the contemporary drama
Jo Dooba So Paar (2011) alongside
Vinay Pathak and
Rajat Kapoor. He played an American whose Italian girlfriend gets abducted in Bihar, India. The film opened to extremely mixed review;
Rajeev Masand from
CNN IBN called it "as boring as watching paint dry," while
Nikhat Kazmi from The Times of India praised it for "holding up a charming mirror on the small town milieu." In early 2012, O'Nell appeared in
Chittagong, The film won three
National Film Awards. O'Nell also appeared in
Shirish Kunder's 2012 film
Joker alongside
Akshay Kumar and
Sonakshi Sinha. O'Nell was seen in
Prawaal Raman's
Main Aur Charles (2015) based on the
Tihar Jailbreak of 1986 during which O'Nell's Richard Thomas was the unwilling accomplice to
Randeep Hooda's
Charles Sobhraj, and eventually became his undoing as the state's-witness in the ensuing trial. O'Nell was praised by Filmfare and Hollywood Director
Michael Hoffman for his "solid supporting performance". O'Nell has appeared in
Bose Dead/Alive (2017,
ALTBalaji miniseries),
Inside Edge (2017;
Amazon Originals series),
Tigmanshu Dhulia's
Raag Desh (2017),
Roohi (2021),
Ae Watan Mere Watan(2024),
Khufiya (2023),
Phule(2025) and
Kesari Chapter 2: The Untold Story of Jallianwala Bagh (2025).
Amazon Prime Video's
Bak Bak starring O'Nell and Divya Dutta is expected to release in 2026.
South Indian cinema His breakthrough role came in 2010 with the Tamil 1940s period drama
Madrasapattinam in which he starred opposite
Amy Jackson and
Arya. The film became the 4th highest-grossing film in
Kollywood that year, despite not faring well outside of Tamil Nadu.
Madrasapattinam was re-released as
1947: A Love Story in
Telugu in August 2011. In 2011, O'Nell was cast in
Santosh Sivan's Malayalam film
Urumi after being recommended by
Madrasapattinam director
A. L. Vijay and his costar Italian actor Sita Spada, his co-star in
Jo Dooba So Paar.
Urumi received widespread critical acclaim, and is considered to be one of the defining films of the
Malayalam New Wave. He teamed up with his A. L. Vijay again for a minor role in
Thaandavam (2012).
Gangster (2014)
and Manglish (2014), both featuring O'Nell alongside South-Indian actor
Mammootty, cemented his position in
South-Indian cinema. He has since appeared in
Lucifer (2019),
SyeRaa(2019),
RRR (2022),
Sweet Kaaram Coffee (2023; Amazon's first Original Series in Tamil) and
Captain Miller (2024), and
L2: Empuraan (2025).
Bengali cinema O'Nell has also worked in the
Tollywood since his debut in 2017 as the main antagonist in
Yeti Obhijaan. His role in
Golondaaj (2021), alongside
Dev Adhikari, earned him a Best Actor nomination from the
West Bengal Film Journalists Association in 2022. His most recent Bengali film
Pokkhirajer Dim (2025) has received commercial and critical acclaim. He will be seen in
Devi Chowdhurani and
Raghu Dakat in late-2025. == Personal life ==