The moves Saturday came after Kirk Gibson, the previous bench coach, was named interim manager following the Thursday night firing of A.J. Hinch.
Porter was in his first season as Arizona's third base coach after five years in the Florida Marlins' organization.
The 58-year-old Youngblood played 14 seasons in the infield and outfield with five major league teams and made the All-Star team with the New York Mets in 1981.
Youngblood was the Diamondbacks' minor league outfield and base running coordinator. He served as a bench coach and third base coach with Milwaukee in 1998.