The accompanying music video will premiere next Friday, March 3.
Trainor also announced that she will be voicing one of the new characters from Smurfs: The Lost Village, SmurfMelody, in the fully animated film.
"I'm so excited to be singing 'I'm a Lady' for this movie," said Trainor. "It's a song that I love and am very proud of, and I can't wait for the world to finally hear it! Getting to play a small part in the film with my character, SmurfMelody, makes this all the more exciting! So happy to be a part of the Smurfs family!!!"
The film will be released in the US on April 7, 2017.