The simple answer to the question of whether you need to include a biographical section in your query letter is: If you’re writing fiction, you do not need to have a bio.
You can always just wrap up your query letter by thanking them for considering the submission. That said, if you have anything to say about yourself (awards you’ve won, organizations you belong to, any publishing credits of any kind, interesting background that pertains to the story), yes, go ahead and list such notes quickly and humbly. They can almost never hurt, and they can certainly help sometimes.
I’ve seen a writer pen a mediocre query, but their bio listed several short stories published with notable publications. At that point, the agent doesn’t even care if the query is poor. The awards won verify that the writer can write.
Jacquie Flynn with Joelle Delbourgo Associates Literary Agency tweeted this advice: