As a teenager, Giannascoli, a Pennsylvania native, wrote and recorded music in his bedroom, producing a sound that channeled the likes of Elliott Smith and Built to Spill. While enrolled at Temple University in 2012, he came to the attention of musician Mat Cothran of Elvis Depressedly, who subsequently shared the homemade demos and approached Giannascoli to play his first live show. The following year, then going by simply Alex G, he signed with the indie label Orchid Tapes, the home of a community of songwriters, including Cothran and Sam Ray (Teen Suicide). He released his home-recorded label debut, DSU, in 2014 and dropped out of school to pursue music.

The U.K. label Lucky Number mastered and released a couple of Alex G's earlier D.I.Y. albums, Trick and Rules, in the spring of 2015, and he signed with Domino Records for his DSU follow-up, Beach Music, issued in October of that year. That album expanded his audience and furthered his reputation, and in 2016 his guitar work appeared on the Frank Ocean albums Endless and Blond. The following spring, with no formal explanation given, he officially adopted the moniker (Sandy) Alex G in time for his second Domino release, Rocket, in May 2017. Still home-recorded, it was a more collaborative effort, featuring members of his touring band, violinist Molly Germer, and prior guest vocalist Emily Yacina. It reached number 23 on Billboard's independent albums chart. Later that year, he appeared on-stage with Ocean and opened shows for Fleet Foxes, amid headlining tour dates. ~ Marcy Donelson & Scott Kerr, Rovi