He joined Pentatonix in 2011, when original members Kirstin Maldonado, Mitch Grassi and Scott Hoying were searching for a bass singer and a beatboxer. The group met the day before the auditions for the third season of The Sing-Off began. The group successfully auditioned for the show and eventually went on to win the title for 2011 (season three). Kaplan acted as the group’s vocal bass, but frequently sang lead parts as well.

As a member of Pentatonix, Kaplan won three Grammy awards. On February 8, 2015, Pentatonix won a Grammy in the “Best Arrangement, Instrumental or A cappella” category for their song “Daft Punk,” a medley of songs by Daft Punk. On February 15, 2016, Pentatonix won a Grammy in the same category, this time for their rendition of “Dance of the Sugar Plum Fairy” from their That’s Christmas to Me album. On February 12, 2017, Pentatonix won a Grammy in the “Best Country duo/group performance” category for their cover of “Jolene,” which featured Dolly Parton.

On April 29, 2017, Kaplan premiered “Fields and Pier,” his first song as a solo artist, under the name “Avriel & the Sequoias.” In May 2017, Kaplan announced that he would be leaving Pentatonix to spend more time with friends and family. His debut EP, Sage and Stone, was released on June 9, 2017.

In October 2019, he announced a European tour, his first since leaving Pentatonix.

On November 5, 2019, he announced an upcoming EP, “I’ll Get By”, set to be released January 24, 2020, along with an accompanying tour. On January 21, 2020, the release was postponed to February 28 as a result of being signed to Fantasy Records.

Avi Kaplan embarked on his first solo live shows with ‘Nashville Residency’ at The Basement in Nashville, TN. It was a series of 5 shows over the course of 3 weeks in April 2019. All 5 shows were sold out. He was accompanied by Daniel Ellsworth (piano/vocals), Jeremy Lister (guitar/vocals), Jonathan Lister (drums/vocals) and Kaleb Thomas Jones (bass guitar/vocals). The Lister brothers and Jones are also members of Street Corner Symphony.

In July 2019, Kaplan began the Otherside Tour which took him to California, Washington State, Oregon. The tour continued in August 2019 going to New York, Massachusetts, Illinois, Missouri, Oklahoma, and Texas. Daniel Ellsworth played an opening set at the Troubour, LA on July 10, 2019 and at the Aladdin Theater, OR on July 15, 2019.

In October 2019, tickets went on sale for Kaplan’s I’ll Get By Tour in Europe and in November 2019, the tickets for North America went on sale. Tour dates have been announced for the Netherlands, Germany, Belgium, the UK, the USA and Canada. In January, 2020, it was publicized that the Indie-Folk duo Paper Wings would be joining Kaplan for the U.S. dates of the tour. During the I’ll Get By Tour in Europe & North America Kaplan was accompanied on stage by Kaleb Thomas Jones (bass guitar/vocals) and Noah Denney (drums/vocals).