Denmark's Thomas Bjorn, who captained Europe to victory over the United States in the 2018 edition, and Italian Edoardo Molinari were named as vice-captains in May.
"My first reaction when Luke asked me was sheer joy," Colsaerts, who played in the winning Europe team of 2012 in Medinah, told the Ryder Cup website.
"Being a vice-captain is a different role to being a player but, nevertheless, my mission in 2023 will be exactly the same as it was in 2012, namely, to make a contribution to the team in any way I can," he added.
The United States won the last Ryder Cup in Wisconsin last year. Europe have not lost a Ryder Cup on home soil since a 15-13 defeat at The Belfry in 1993.
The 2023 Ryder Cup will be played from September 26th to October 1st.
Former world number one Donald played with Colsaerts in the 2012 edition.
"Nico gets along extremely well with all the guys out here on the DP World Tour and he will be a great person to help keep an eye on things here in Europe in periods when I might be in the US," he said.
Donald was appointed captain in August, replacing Henrik Stenson who was stripped of the role before joining the LIV Golf Invitational Series.
