Mollie O'Brien (born October 25, 1952) is an Americana, bluegrass, R&B, and folk singer from Wheeling, West Virginia. She has released a number of Americana albums with her brother, Grammy-winner Tim O'Brien. She has also released five positively received solo albums. She is currently based in Denver, and regularly tours and performs with her husband, guitarist Rich Moore, as a duo. Together they have released three studio albums: Saints and Sinners (2010), "Love Runner" (2014), "Lost In the Crowd" (2025) and a live CD, 900 Baseline. They also released an album with their daughters, aptly titled "Daughters" (2015.) She has regularly appeared on shows such as A Prairie Home Companion, Mountain Stage, and contributed vocals to the Grammy-winning album True Life Blues: The Songs of Bill Monroe. She is known for her interpretations of classic songs by artists such as Tom Waits, Memphis Minnie, Willie Dixon, Chuck Berry, Si Kahn, Terence Trent D'Arby, and Kate MacLeod.

Mollie O'Brien was born October 25, 1952, and raised in Wheeling, West Virginia, where she was the second youngest of five siblings. Her family was immersed in music, and her mother frequently drove Mollie and her younger brother Tim to local performances by 1960s musicians such as The Beatles, Wheeling Symphony, Count Basie, Dave Brubeck and Ray Charles.

She has stated her brother bringing home the Ray Charles album What'd I Say was influential, and she loved music on AM radio such as "The tail end of doo wop, all that stuff in the '60s you still got to hear before the total transformation of pop music that decimated those people. I soaked up everything." At a young age she sang along with the Lawrence Welk show, and at age 11, learned to play piano and sing "Anchors Aweigh" in tribute to her older brother, then a Naval Academy midshipman.

O'Brien attended Catholic schools. In high school, she and her brother Tim began playing Peter, Paul, and Mary songs as a duo at church and local coffeehouses. She also began listening more avidly to singers such as Joni Mitchell, Bonnie Raitt, Dinah Washington and Frank Sinatra. After several years as a folk duo, Tim moved to Denver, Colorado, to join the bluegrass group Hot Rize. She moved to New York City for 4 years, then back to Wheeling WV for 2 years before finally settling in Colorado in 1980.

O'Brien studied voice and theater in college, and after her sophomore year, moved to New York City to spend four years attempting to make it in 1970s Broadway. She eventually took a job in New York City's garment center, where she has stated the locally diverse styles on the radio helped further expose her to new styles. She has quoted "They played old blues and folk music, which to my knowledge, no one was playing [elsewhere on the radio]."

In 1976, her brother and close friend Tim was still living in Colorado as a bluegrass and folk musician, and playing in the Ophelia Swing Band. O'Brien gave the band a place to stay when they played a gig in New York City. "They just completely turned me on end. And I said, 'I have to sing," she recalls. She eventually accepted Tim's invitation to move there, and began singing and earning a living in local Denver and Boulder bars on the R&B and jazz club circuits.

On April Fool's Day 1981 she met guitarist Rich Moore at the Denver Folklore Center. He and O'Brien married in 1983, and formed the R&B band The Late Show, with Moore on bass. After having two daughters soon after marriage, Moore elected to stay home and work a day job as they raised the children.

In 1984, O'Brien and her brother Tim reunited for a Mother's Day concert, and four years later recorded the duet album Take Me Back. Chip Renner of AllMusic gave the album 4.5/5 stars, and called it "a masterpiece." In 1986 they began performing again as an Americana duo, and produced two more albums, Remember Me (1992), and Away Out on the Mountain (1994). All three records were released on Sugar Hill Records.