The competition-winning scheme, which would have created 35,000m 2of education facilities and student accommodation, was rejected by the council's planning committee, ending years of speculation about the controversial project.
The move has delighted local groups who have fought an intense battle to stop the development - the first stage of a 10-year plan to bring together a number of Middlesex University's existing campuses on the site.
As well as branding the scheme 'overambitious', campaigners also had issues over the proposed development's impact on the green belt and claimed the plans were 'not consistent' with the historic buildings already in Trent Park.
Project architect Katherine Tombling said she was saddened, but not surprised, by the decision, which leaves the university's consolidation plans in tatters.
She said: 'We thought we had a good chance of getting through, so the decision came as a disappointment. But we know there was a lot of local pressure and there was a group of people who were actively campaigning against the scheme.
'It wouldn't have mattered what scheme we'd proposed, they wouldn't have revised their view that they didn't want a university in the park.
'This revised masterplan went ahead with the full approval of English Heritage and we have got the optimum scheme for this site,' she added.
It is understood the university is now considering whether to appeal against the decision.
BDP was originally appointed to draw up proposals for the Trent Park site after seeing off competition from HOK, Pascall + Watson, Sheppard Robson and YRM.