Molly was born October 8, 1993 in Texarkana, Texas. She attended St. James Day School from kindergarten until the sixth grade. While the school "fostered creativity", Molly's talent was also encouraged at home. "I guess you couldn't stop me from entertaining since I was three. My Dad had a boy scout troop and I was always with them since my mom worked a lot...I was everyone's baby. I went to nursing homes and played my scratchy violin. I loved entertaining no matter where it was." She started acting lessons when she was 7 and got into the business at 13.
She remembers begging her parents for an agent when she was 12 and they finally agree to let her attend a camp for children who wanted to act, thinking she'd "get it out of her system." A well-known agent was at the camp: "She stood in front of everyone and said, 'Raise your hand if you want to be famous.' Pretty much everyone raised his or her hand, but me. I thought that’s not why I want to act. Then she said, 'Raise your hand if you want to do this because you want to be super rich.' And all these kids raised their hands, but again I didn’t. I thought I would be totally happy with not making any money from this. Then she said 'Raise your hand if you didn’t raise your hand for any of those questions.' My hand was the only hand that rose, and pretty much everyone hated me...we had that connection. And that’s what it takes. I constantly remind myself of that and it keeps me grounded." She also says she lives by the mantra of "Do or do not. There is no try" because an actor has to be prepared for anything if they really want a career in show business.
When asked what advice she would give to a young actress looking to get into the business, she said "Write down your goals, figure out what you want to do, and then go for it with heart and drive, then there's no limitation to what anyone can achieve."
She considers co-star and on-screen father Nathan Fillion to be like a second father while shooting Castle, with her real-life father back home in Texas.  In an article for TV Guide, she added "My Dad's the best, but if I couldn't have him, I'd take Nathan. He's that kind of wonderful."
Molly has said she most enjoys the positive relationship between Richard Castle and his daughter Alexis and likens her character to "a rubix cube. Just when I think I have her down and I'm just about to put her in a little box she does something to switch me up."
When asked how she is similar to and different from Alexis, she said: "I like to say that we’re similar in that we both have great relationships with our dads...I’m a daddy’s girl, all the way. We both use our imaginations. She plays laser tag, I play laser tag. These very physical things we both like, like karate and going to the gym or rifle ranges, things like that...Ways we differ used to be very big...we’re really becoming parallel. I’m really feisty, I don’t back down if I’m confronted, basically, whereas Alexis was always very demure and very, 'Oh, I have to study for this test.' She’s still very smart, but she’s becoming, I guess a little later than I became, a little more street smart, a little more savvy to what people are saying and what they actually mean. Like when she hit the girl in the bathroom [in Slice of Death ]...we’re starting to become very similar in a feisty way, which I like to see...I would like to see her go into work with Lanie Parish in a medical field or maybe even a private eye, via the Veronica Mars route...Who doesn’t love Veronica Mars?"
- Jen in Avalon High (2010)
- Belinda Cratchit in A Christmas Carole (2009)
- Paula in My One and Only (2009)
- Esmee Johnson in The Sacrifice (2008)
- Teen with Pinups in Walk Hard: The Dewey Cox Story (2007)
In November 2011, shooting will begin on Molly's most recent project, an independent film retelling of the Hansel and Gretel fairytale entitled Black Forest: Hansel and Gretel and The 420 Witch. Molly and Twilight star Michael Welch will play the endangered brother and sister and Lara Flynn Boyle will play the witch.
- Castle is her first role on a TV series.
- Is 5' 4" tall.
- Admires Philip Seymour Hoffman, Jodie Foster, Meryl Streep, Robert Downey, Jr., Daniel Day-Lewis, Cate Blanchett and Forest Whitaker.
- Has twice played daughter to a character portrayed by actress Darby Stanchfield, first in The Sacrifice, and second in Castle episode 1.6, Always Buy Retail when Darby played Richard Castle's first wife Meredith.
- Had three speech impediments as a child.
- Enjoys surfing, playing the violin, cooking, and playing with her teacup Yorkshire Terrier named Piper.
- Her mother has a medical background.
- Would love to see Rainn Wilson guest star on Castle
- Is a green belt in karate
- Interview with Molly C. Quinn, StanaKatic.com newsletter, March 2011
- AssignmentX.com "It's all in the family for Castle stars Susan Sullivan and Molly Quinn." By Abbie Bernstein. Posted 3 January 2011
- Head Shot Magazine interview June issue, posted June 10, 2001
- Molly C. Quinn quoted at "An Evening with Castle" at The Paley Center for Media, March 16, 2010
- "What's Next for Castle's Crew", page 19, TV Guide, Feb. 28-March 6, 2011
- Comic-Con 2011: Castle interviews with Nathan Fillion, Seamus Dever, Jon Huertas, Molly Quinn, and Executive Producer Laurie Zaks by Dave Trumbore, Collider.com, posted July 27, 2011
- Indies light up The 420 Witch, written by Jeff Sneider, Variety.com, posted October 7, 2011
- Biography of Molly C. Quinn at the Internet Movie Database 
- "A Conversation with Castle's Molly Quinn, TV.com interview by Stefanie Lee, posted March 8, 2010 
- " Castle Star Molly Quinn Calls the Season Finale "Phenomenal" and "Crazy" Wetpaint.com, written by Ian Spiegelman, posted April 14, 2011