Uchihira Mio was born in Tokyo. After graduating from a junior college in Tokyo, she worked at a publishing distribution company. While working, she attended the Tokyo Copywriter Training Course. Afterwards, she aimed to become a screenwriter and studied at the Scenario Center. Through participating in the TV Asahi 21st Century Newcomer Scenario Contest, she has reached her current position.
In 2007, she won the highest award, the Araiichi Award, organized by the Scenario Center. In 2008, she reached the final selection stage of the 14th Scenario S1 Grand Prix and she received an honorable mention at the 15th Scenario S1 Grand Prix.
In 2010, she reached the final selection stage of the 10th TV Asahi 21st Century Newcomer Scenario Grand Prize. In 2013, she received an honorable mention at the 25th Scenario S1 Grand Prix.