Giannascoli was born on February 3, 1993, in
Havertown, Pennsylvania, a
Philadelphia suburb. His father's family originates from
Abruzzo in
Southern Italy. At age 11, he learned how to play the guitar that his older brother gave him and began recording music. While attending
Haverford High School, Giannascoli made two albums that he shared with friends. He experimented with different musical styles while making collaborative music. This included the "
goth techno" he made with his sister in their band MOTHER, The Scoli Xtreme with his older brother, as well as the projects involving his high school band The Skin Cells, described as "
pop rock that accidentally ended up being
punk". After self-releasing various albums,
EPs, and singles on Bandcamp from 2010 to 2012, Giannascoli's popularity spread through word of mouth, blogs, and reverence by other musicians.
The Fader called Giannascoli "the internet's secret best songwriter." Following the release of the album, Giannascoli went on tour throughout North America and Europe. In 2014, Giannascoli signed with
Domino Recording Company and released his debut with the label
Beach Music on October 9. The following year, Giannascoli worked with
Frank Ocean on his albums
Endless and
Blonde, providing guitars and arrangements for several songs. He also joined Ocean's live band on guitar for his 2017 tour. On March 2, 2017, Giannascoli announced that his second album with Domino, titled
Rocket, would be released on May 19 and shared the first two singles, "Bobby" and "Witch". On April 4, Giannascoli announced the change of his stage name from Alex G to (Sandy) Alex G, with no further explanation, and shared another single from the album, "Proud". The music publication
Spin attributed the name change to a legal conflict with singer and YouTuber Alex Blue, who was operating at the time under the trademarked name "Alex G". On choosing the name 'Sandy', Giannascoli said it "was the first thing [he] put on Bandcamp" and that he had "just used that 'Sandy' as a sort of [social media] tag" since then. On May 4, he released two more singles, "Brick" and "Sportstar", before the release of the album.
Rocket received acclaim from music critics and appeared on multiple publications' year-end lists of the best albums of 2017. Giannascoli's eighth studio album,
House of Sugar, was released on September 13, 2019. The album received positive reviews and placed 17th on
Pitchfork's year-end best albums list. In June 2020, he dropped "(Sandy)" from his stage name, returning to going by Alex G. Giannascoli scored the film ''
We're All Going to the World's Fair'', released on April 8, 2022. Giannascoli also scored
Jane Schoenbrun's film
I Saw the TV Glow, which was released by
A24 in 2024. Giannascoli's ninth studio album,
God Save the Animals, was released on September 23, 2022. In January 2024, Giannascoli announced his signing with
RCA Records and an upcoming tour supporting the band
Foo Fighters. He contributed to eight tracks on
The Great Impersonator by
Halsey. On May 2, 2025, Alex G performed a 30-minute set at
Bernie Sanders' "Fighting Oligarchy: Where We Go From Here" rally held at the
Pennsylvania Farm Show Complex & Expo Center in
Harrisburg, Pennsylvania. In late May 2025, Giannascoli announced his tenth studio album and RCA Records debut
Headlights, which was released on July 18. ==Musical style==