Underweight Russell disqualified after Belgian Grand Prix win
A technical report released after the race said Russell's car was found to be 1.5kg below the minimum weight limit for car and driver combined.
"Car 63 is disqualified from the race classification," the stewards announced in a statement.
"All other drivers move up in the classification," they added.
The 26-year-old Briton started in sixth place on the grid before edging Hamilton in second and McLaren's Oscar Piastri who came third.
Russell drove the 44-laps race with only one pit stop which led to him going 34 laps on his second set of tyres, a strategic decision taken during the contest enabling him to take the lead and an unexpected third career victory.
"Heartbreaking," Russell said on social media.
"We came in 1.5kg underweight and have been disqualified from the race.
"We left it all on the track today and I take pride in crossing the line first.
"There will be more to come," he added.
Russell's car was initially weighed at 798kg, which is exactly on the minimum weight limit for car and driver combined.
But stewards found the car had not been fully drained of fuel.
"The car was weighed again on the FIA inside and outside scales and the weight was 796.5kg," the statement said.
"The calibration of the outside and inside scales was confirmed and witnessed by the competitor."
As a result, Russell's teammate Hamilton now takes the victory, the 105th of his career and second of the season.
Piastri takes second while Ferrari's Charles Leclerc moves on to the podium in third.