Winslow was born into a family of actors: he is the son of actors Michael Fegley and Merce Tonne, and brother to actors August Fegley and Oakes Fegley.

Winslow developed his skills in 2017 while starring in the stage production of A Billion Nights on Earth, a production he also added creative collaboration to, with avant-garde theatre director Thaddeus Phillips. The show was developed at the Buntport Theatre in Denver, CO, over the summer of 2017, then toured to sold out houses in Philadelphia in September 2017, and was featured as part of the Next Wave Festival at the Brooklyn Academy of Music in November that year, where it again sold out its run.