The former Argentina international, who played for clubs including Manchester United, Real Madrid and Paris Saint-Germain, was unable to convert his top-level experience into success on the touchline in MLS.
Heinze departs after his team won just two of their opening 13 games in the regular season, losing four and drawing seven times to sit 10th in the 14-team Eastern Conference.
Gabriel Heinze Relieved of Duties as Atlanta United Head Coach.— Atlanta United FC (@ATLUTD) July 18, 2021
Club President Darren Eales and Vice President and Technical Director Carlos Bocanegra to address the media at 4pm today.
A 1-0 defeat to New England on Saturday sealed Heinze's fate.
He was appointed in December 2020, and a recent stand-off between the coach and star player Josef Martinez, a former MLS Cup MVP, went down badly with supporters.
A statement from the club said: "Atlanta United today announced the club has relieved head coach Gabriel Heinze of his duties, effective immediately. Assistant coach Rob Valentino will take over as interim head coach.
"A variety of issues relating to the day-to-day leadership of the team led the club to this decision."
Club president Darren Eales said: "This was certainly not a decision we wanted to make at this point in our season, but it was the right one for the club. Gabi is a talented coach and is undeniably passionate about his craft and the sport of soccer."