---
name: "Thomas Philip O'Neill"
canonical: "https://film.one/person/thomas-philip-oneill"
roles: []
reviewed_on_fi1m: 1
average_over: 1
updated: "2026-09-17T13:42:59.909289+00:00"
licence: "© Fi1m Ltd. Written by AI under a human editor; checked against sources before publication. Quote with attribution and a link to the canonical URL."
---

# Thomas Philip O'Neill

Actor. Born in Boston, Massachusetts.

## Details

- **Elsewhere:** https://www.imdb.com/name/nm4420814/, https://www.themoviedb.org/person/1745901

## Streaming the US now

- **Netflix:** [*MINDHUNTER*](https://film.one/tv/mindhunter.md) (83)

For United States; add `?region=XX` for another country.

## Biography

Thomas Philip O'Neill is an American actor. Originally from Boston, he trained at New York University’s Tisch School of the Arts, receiving a BFA through the Stella Adler Studio, the Experimental Theatre Wing and the International Theatre Workshop in Amsterdam. He also studied at the British American Drama Academy in London and later apprenticed at Stella Adler Studios under master teacher Alice Saltzman.

O’Neill is known for his role as Leo Buchanan in the Netflix series *Mindhunter* (2017). He has appeared as Dr Neil Mosbach in the CBS series *FBI* (2018–), as well as in *Black Mass* (2015), *Mapplethorpe* (2018) and guest roles in *The Blacklist*, *Law & Order: Special Victims Unit* and *NCIS: New Orleans*. He is the grandson of former Speaker of the House Tip O’Neill.

*Sources: imdb.com, watch.plex.tv.*

## On Fi1m (1)

- *MINDHUNTER* (2017), Fi1m 83, as Leo Buchanan — [page](https://film.one/tv/mindhunter.md)

## Complete filmography (11)

Every credit, newest first. Titles without a page can be requested for review on the HTML page.

- *The Mix* (2026), as Sean Palermo
- *Writer's Block* (2025), as Matthew
- *The School Duel* (2024), as Pastor Mark
- *Endless Sea* (2022), Acting
- *Mapplethorpe* (2019), as David Croland
- *FBI* (2018), series, as Neil Mosbach, Dr. Neil Mosbach
- *MINDHUNTER* (2017), series, as Leo Buchanan — Fi1m 83, [page](https://film.one/tv/mindhunter.md)
- *Black Mass* (2015), as FBI Wire Tech
- *NCIS: New Orleans* (2014), series, as Eddie Oberman
- *Law & Order: Special Victims Unit* (1999), series, as Rick Donnelly
- *Law & Order* (1990), series, as Dr. Neil Mosbach

---
© Fi1m Ltd. Written by AI under a human editor; checked against sources before publication. Quote with attribution and a link to the canonical URL. Canonical: https://film.one/person/thomas-philip-oneill