In a flurry of messages on his X platform, Musk also renewed his criticism of British Prime Minister Keir Starmer, highlighting that his time as chief state prosecutor in England and Wales coincided with the emergence of a child grooming scandal.
It comes after Musk, the world's richest man and key ally of US President-elect Donald Trump, faced recent criticism over his support for Germany's far-right AfD party.
Concerns have also emerged in Britain over claims that Musk is set to donate tens of millions of pounds to the upstart hard-right, anti-immigrant Reform UK party, led by Nigel Farage.
Musk has been highly critical of Starmer, including during anti-immigration riots that rocked English and Northern Irish cities last year.
In his overnight X posts, Musk claimed Robinson was in prison "for telling the truth" and that "he should be freed".
His posts swiftly garnered huge support from far-right figures, including Dutch politician Geert Wilders, as well as some right-wing YouTube channels.
- Grooming scandal -
Robinson, a one-time football hooligan who boasts a string of UK criminal convictions, is serving an 18-month jail term for repeated contempt of court breaches.
He has amassed a big online following after years spearheading a vehemently anti-Muslim and anti-immigrant movement.
Accused of helping fuel last summer's riots, Robinson was jailed in October after he admitted committing contempt of court over a long-running libel case involving a Syrian refugee.
However, Musk's messages Thursday focused on Robinson's long-time highlighting of historical scandals involving pedophile grooming gangs in northern English cities.
The widespread abuse of girls, which emerged more than a decade ago in a number of English towns and cities including Rochdale, Rotherham and Oldham, has long stirred controversy.
A series of court cases eventually led to the conviction of dozens of men, mostly of South Asian Muslim origin. The victims were vulnerable, mostly white, girls.
Subsequent official reports into how police and social workers failed to halt the abuse found that officials in some cases turned a blind eye to avoid appearing racist.
The scandals have been seized upon by far-right figures, in particular Robinson.
- Inquiry calls -
Sharing various other accounts' claims around the decades-spanning crimes, Musk noted that the Crown Prosecution Service (CPS) decides whether to charge suspects.
"Who was the head of the CPS when rape gangs were allowed to exploit young girls without facing justice? Keir Starmer, 2008-2013," he posted.
Starmer was the head of the CPS in that period, but none of the probes into the scandals singled him out for blame or found that he tried to block prosecutions due to concerns over Islamophobia.
In 2012, Starmer blamed the justice system's flawed approach to sexual exploitation and ordered a comprehensive restructuring of the CPS's responses to it.
Musk has also criticised Jess Phillips, safeguarding minister since July, following reports she has rejected calls for a public inquiry into the grooming scandal in Oldham, northwest England.
Following a backlash from some UK opposition lawmakers to the reported decision, Musk posted Wednesday that "she deserves to be in prison".
Kemi Badenoch, the leader of the Conservative Party -- in power from 2010 to 2024 but now the official opposition -- on Thursday backed a wider public inquiry "into the rape gangs scandal".
"Trials have taken place all over the country in recent years, but no one in authority has joined the dots," she said.
© Agence France-Presse
