Seol In-ah made her acting debut with a cameo role in the 2015 KBS2 series The Producers. She began to gain attention with her appearances in the 2017 dramas Strong Woman Do Bong-soon and School 2017, which aired on JTBC and KBS2, respectively. Also in 2017, she received the Female Rookie Award at the MBC Entertainment Awards for her work as a host of the entertainment news show Section TV.  In 2018, she was cast in her first leading role in the KBS1 daily series Sunny Again Tomorrow, which won her Best New Actress at the KBS Drama Awards. This was followed by a supporting role in the 2019 MBC social satire drama Special Labor Inspector Jo. Later in 2019, she led the KBS2 romantic comedy Beautiful Love, Wonderful Life, which earned her an Excellence Award at the KBS Drama Awards. In 2020, she joined the cast of the hit tvN fusion sageuk series Mr. Queen.

Seol In-ah majored in acting at the Seoul Institute of the Arts.