The film--the director's debut--topped the field of 15 finalists, selected out of a total 2,000 entries in the Generation category of youth-themed films.
"Mellow Mud" has been received positively by critics, with the Hollywood Reporter praising the talented young leads and calling the film a "delicate drama about an often anguished time of life, all handled with sensitivity".
"Of course it was a very pleasant surprise. What more can I say?" the director told Latvian Radio (LR).
While movie critic Daira Āboliņa told LR that with the film "Latvia is losing the status of a small, unknown movie country."
The film premieres in Latvia February 26.