In February 2018, Saint Jhn released "I Heard You Got Too Litt Last Night". He also released another new song, "Hermes Freestyle". In October of that year, he played at two festivals, Rolling Loud and the Voodoo Experience. The following month, Saint Jhn released another original track, "3 Below". In February 2017, Jidenna's album, The Chief, was released featuring the song, "Helicopters / Beware", which Saint Jhn co-wrote. In October 2016, it was announced that Saint Jhn would open up for Post Malone during a run of shows on the West Coast. He followed that with two more songs in 2016, " Roses" and "Reflex". Also in 2016, he released his first song under the moniker, Saint Jhn, entitled "1999". In 2016, he earned a writer credit for the Usher songs, " Crash" and " Rivals", both of which appeared on the Hard II Love album. In the following years, Saint Jhn wrote songs for Kiesza, Gorgon City, and Nico & Vinz, among others. After returning home, Saint Jhn co-wrote the 2012 Hoodie Allen song, "No Interruption". For two months, he wrote songs for Rihanna, but none of his records were accepted.
Soon after, he was flown to Los Angeles, California by music executive Zach Katz. John Portfolio, and a mixtape, In Association, under his birth name.
Prior to adopting the Saint Jhn stage name, he performed and wrote using his birth name, Carlos St. He wrote his first song in his first year of high school while living in Guyana. He began creating music when he was twelve years old and was inspired by his older brother, who would rap in the neighborhood with friends. Growing up, he split his time in three year intervals between Guyana and the neighborhood of East New York in Brooklyn. Phillips was born in Brooklyn, New York and raised in Georgetown, Guyana.