A bench headed by Justice Swatanter Kumar government's plea on the ground that the Supreme Court has also junked a similar plea.
The Green panel said that the Ministry of Road Transport and Highways, which had sought modification of NGT's April 7, 2015 order, did not file any review plea and moved the Tribunal "in the guise of seeking modification".
The bench which delivered the judgement also comprised Justices Jawad Rahim, R S Rathore and one expert member B S Sajwan.
The Centre had earlier opposed the ban, saying there was a "misconception" that only diesel pollutes the environment.
The Green panel had issued an order last year directing the Delhi RTO to deregister all diesel vehicles operating in the city that are over 10 years old.