Mayor Sadiq Khan's Greater London Authority has given activists permission to launch the bouncing behemoth from Parliament Square Garden on July 13 - the day after President Trump is set to arrive in London for a four-day visit to the United Kingdom.
The mayor's office, at first, did not recognise "Trump Baby" as a legitimate protest, the demonstrators said.
However, he said City Hall had "rediscovered its sense of humour - Trump Baby will fly".
Protesters are planning to fly a blimp over parliament portraying Trump as an orange, snarling baby during his visit after Khan approved a request for its use.
A spokesperson for the mayor said: "The Mayor [sic] supports the right to peaceful protest and understands that this can take many different forms".
Restrictions mean that it would not be allowed to fly more than 30 meters (98 feet) off the ground, Sky News reports.
Thousands are expected to protest in London on Thursday and Friday against the president's working visit.
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The next day, Trump and May will visit an unspecified defense site before holding talks at Chequers, the prime minister's country retreat 40 miles (65 kms) from the capital.
Continuing the military theme on Friday, the president and Theresa May will watch a demonstration at a defence site to showcase the UK's "cutting edge military capabilities and integrated UK-US military training".
May invited Trump for a formal state visit after she met him in Washington shortly after his inauguration.
In response to the news, former UKIP leader Nigel Farage tweeted that the balloon protest would be "the biggest insult to a sitting US President ever", apparently forgetting the four Presidents who have been assassinated and the racist birther campaign against President Barack Obama which Trump fuelled.
There are rules that the Trump baby blimp must abide by, however.
Khan has been openly critical of President Trump, and he was also the subject of one of Trump's Twitter attacks last summer.
According to the CrowdFunder page, the group has raised far more money than they need to make Trump fly, and now the focus is on starting the Trump baby world tour.