Weatherwax was born in Engel, Sierra County, New Mexico, the son of Anna Elisa (née Wallis) and Walter Smiley Weatherwax. Pal became a movie star through a weather-related event. MGM, which had decided to use a show collie trained by Frank Inn in the movie, took advantage of a massive flooding of the Sacramento River in northern California to obtain some spectacular footage for the film. Their fancy collie was still in training, so MGM hired Pal as a stand-in for the river scene. Although the work was actually considered complicated for an animal actor, the dog performed exceptionally well.
According to legend, after seeing the first prints, the head of MGM, Louis B. Mayer, stated that "Pal had entered the water, but Lassie had come out," and a new star was born.