In the early 2000s she began appearing in guest-starring roles on a number of television dramas and comedies, including The Drew Carey Show, The X-Files, ER, Frasier, The West Wing, NCIS, Medium, Grey's Anatomy, Private Practice, Two and a Half Men, Supernatural, Drop Dead Diva, and Castle.

Agnes Hunt in 2002, on NBC period drama American Dreams as Diane Shaw in 2003, on NBC's Scrubs as Dr. Grace Miller in 2004, as Assistant State Attorney Monica West on CBS's CSI: Miami (2005–06), and on ABC primetime soap opera Dirty Sexy Money (2008–2009) as Ellen Darling, the eldest daughter-in-law of the Darling family.

[11][12] Young has appeared in supporting roles in a number of films, including We Were Soldiers (2002) and Mission: Impossible III (2006), along with independent movies like Larceny (2004), Eve of Understanding (2006), Trust Me (2007), This Is Not a Test (2008), In My Sleep (2010), The Freebie (2010), and Joint Body (2014).

In 2011 Shonda Rhimes cast Young in the recurring role of First Lady, then 2016 Republican presidential nominee, Melody "Mellie" Grant on the ABC political thriller television series Scandal opposite Kerry Washington and Tony Goldwyn.

[19][20] Cicely K. Dyson's review for The Wall Street Journal states: "Bellamy Young has been an amazing scene stealer for two-and-a-half seasons, and this time she finally got her chance to shine.

"[21] Robert Rorke, writing for The New York Post states, "In Mellie, the show has its most fleshed-out character and in Young, its most compelling performer.

[23] In 2016, she starred in the crime drama film The Night Stalker directed by Megan Griffiths about the serial killer Richard Ramirez.

[24][25] The following year, she had a supporting role in the independent comedy film Bernard and Huey opposite Jim Rash and David Koechner.

[26][27] In 2018, she co-starred in Disney's live action adaptation of A Wrinkle in Time, along with Oprah Winfrey, Reese Witherspoon, and Mindy Kaling.

[29] In March 2019, Young announced that she would be co-starring in the Fox drama pilot Prodigal Son opposite Michael Sheen, Lou Diamond Phillips, and Tom Payne.

In November 2022, she was cast in the Hulu mystery thriller series The Other Black Girl, a television adaptation of the 2021 novel by Zakiya Dalila Harris.

[47] For International Women's Day 2020, Young directed a PSA, for CARE; she appears as well as Kerry Washington, Shonda Rhimes, and Katie Lowes.