The Ukrainian President had wanted to record a video for contestants, and the global audience of up to 200 million people, during Saturday night's final in Liverpool.
Volodymyr Zelenskyy has been barred from delivering a message at the Eurovision Song Contest final, which is being hosted this year by the UK on behalf of Ukraine.
Organisers say there are rules in place to keep politics out of the singing competition.
In a statement, the European Broadcasting Union (EBU), which produces the event, said it had declined Zelenskyy's request to address the audience - which can be up to 200 million viewers around the world - though noted his "laudable intentions".
"The Eurovision Song Contest is an international entertainment show, and governed by strict rules and principles which have been established since its creation," the EBU statement says.
"One of the cornerstones of the Contest is the non-political nature of the event."
"This principle prohibits the possibility of making political or similar statements."
Ukrainian rap group "Kalush" won the contest last year, amid a surge of public support from voters around Europe.
Normally, the winning country hosts the next edition of Eurovision. But Ukraine could not do so because of the Russian invasion. At the 2022 runner-up, the UK took the helm, with the BBC helping to organise the event in Liverpool.
BBC insiders reportedly told The Times newsaper that "difficult and delicate" negotiations were ongoing, with Eurovision organisers fearing the ramifications of rejecting Zelenskyy's request to speak at the final.
The decision has drawn criticism in some quarters, who claim the war-torn country should morally be given the opportunity to speak out against Russian aggression.
The possibility of Zelenskyy's address was considered "unacceptable", as of the morning of 12 May.
Public appearances and speeches by the Ukrainian President are widely seen as having played an important role in helping the county rally public sympathy and secure Western support.
Ukrainian artists, including last year’s winners Kalush Orchestra, will be performing or featuring in either the two semi-finals or Grand Final.
Planned guest appearances by Zelenskky have caused controversy in the past, with a group of Italian politicians arguing his speech at the country's Sanremo Music Festival was too political.