Sadowitz, known for his controversial stand-up as well as his skills as a magician, is opening his latest show in London with a video appeal from the mother of the late actor Mark Blanco.
Mr Blanco, 30, died in 2006 after falling from the first floor balcony of a London flat where Doherty, known for his bands Babyshambles and The Libertines, and friends were having a party.
A campaign to discover what exactly happened that night is being led by Mr Blanco's mother, Sheila, after an inquest delivered an open verdict.
Mr Blanco and Sadowitz, who is currently performing at the Leicester Square Theatre in London, became friends after meeting at a convention for magicians.
Sadowitz, who grew up in Glasgow, is now helping Sheila Blanco's seven-year campaign for a full investigation into her son's death.
In the video, which Sadowitz shows to audiences before his performance begins, she says: "Funds are desperately needed to expose this miscarriage of justice."
This week, Sadowitz spoke about the campaign to discover the truth about the death of "one of my best friends" and "a potentially great author, wit and unique talent."
He said: "It's good that the audience sees that message from Sheila as a separate thing.
"It's pretty disturbing that there was no investigation. It was swept under the carpet."
The events on the night of Mr Blanco's death have long been unclear, but in December 2012 BBC Newsnight commissioned analysis of CCTV footage of the fatal fall, revealing another figure on the balcony and concluding that Mr Blanco was "probably dropped".
Mr Blanco was found dying on the street with extensive head injuries.
He was due to play the lead in a new play that week and was keen to get some extra publicity for the production, and had apparently gone to the party to alert Doherty's interest.
The Cambridge graduate, who once worked for Goldman Sachs, visited the flat of Paul Roundhill, a friend of Doherty, in an attempt to publicise the play, Accidental Death Of An Anarchist, by Dario Fo.
Doherty's minder Johnny Jeannevol, known as Headlock, later confessed to police that he had pushed Mr Blanco over the balcony.
However, he later retracted the statement, while police concluded his death was suicide - a likelihood since ruled out by the coronor - or an accident.
An inquest into the death in 2007 heard that Doherty asked Jeannevol to "have a word" with Mr Blanco after he had "annoyed" him.
Doherty was also apparently seen on CCTV running away from Mr Blanco's body.
Sadowitz said: "Everything surrounding that flat and the people in it seems well protected."
Injuries to Mr Blanco's face suggest he had been punched and evidence gathered by the campaign suggests he did not jump intentionally.
The inquest recorded an open verdict, rejected suicide and the coroner called for a fresh investigation. Scotland Yard has referred the case to SCD1, its specialist crime division, but has not reopened the case.
Sadowitz said he would continue to back the cause and added: "You have to at least try. You can't let the details disappear. This was a really decent guy, a good guy.
"What Mark's mum is doing is unbelievable: she's got a mountain to climb."