The Celtics' announcement occurred after the under-seven timeout break in the first quarter of the team's home game against the Los Angeles Clippers on Thursday.
Boston also released a statement in conjunction with the video:
Garnett helped lead the Celtics to the 2007-08 championship, ending a 21-year title drought for the franchise. He averaged 15.7 points and 8.3 rebounds per game for the C's from 2007 to 2013, earning five All-Star appearances, winning the '07-'08 Defensive Player of the Year and making an All-NBA first team.
The Celtics made the playoffs during each of his seasons with the franchise and reached the NBA Finals twice.
Boston's Big Three of Garnett, Paul Pierce and Ray Allen helped lead the 2007-08 Celtics to a 66-16 record, which is the team's third-best mark in a storied history that features 17 championships.
The surefire future Basketball Hall of Famer made 15 All-Star teams, garnered nine All-NBA selections and won the 2003-04 MVP in a career that spanned from 1995 to 2016. The Minnesota Timberwolves drafted him No. 5 overall out of Farragut Career Academy, and he played for the Wolves until a trade sent him to Boston.
Garnett's career came full circle as he finished it with Minnesota in 2016.
The man known as KG said the following in the Celtics' statement, per Tim Bontemps of ESPN.
"I'm honored and thankful to have my number retired with the Celtics. I will always have immense respect and appreciation for ownership, Danny Ainge, Doc Rivers, my past teammates and Celtic Nation!"
A date for Garnett's jersey retirement ceremony has not yet been announced.