Greville Janner, a member of the upper House of Lords, had been suffering from such severe dementia that a judge ruled earlier this month that he was unfit to enter a plea.
A rare so-called “trial of the facts” was therefore set to take place in April — but his death means it no longer will.
“This is devastating news for my clients,” said lawyer Liz Dux, who represents six of Janner’s alleged victims.
“They have waited so long to see this case come before the courts. To be denied justice at the final hurdle is deeply frustrating.
“Worse still is that so many opportunities to bring this matter to justice whilst he was well were missed.
“All they have ever wanted is to give their evidence in court and have these very serious allegations tested and to be believed.”
Janner is one of a number of high-profile figures to face historic sex abuse charges in Britain after BBC presenter Jimmy Savile was revealed as a serial paedophile following his death in 2011, leading a rush of victims to come forward.
Janner was a Labour MP for the central English city of Leicester between 1970 and 1997.
He was accused of 22 offences dating between the 1960s and the 1980s against nine alleged victims, eight of whom were aged 16 or under at the time.
State prosecutors had initially declined to bring charges against Janner due to his condition, a decision that provoked an outcry and was later reversed.
In a hearing in August, Janner spent just 59 seconds in the dock.
Due to the severity of his dementia, a “trial of the facts” was scheduled. In such trials, a jury simply decides whether the defendant committed the acts alleged. There is no decision on guilt, or possible conviction.
Janner’s family has strongly denied claims that he used his power as a member of parliament to abuse vulnerable boys at a Leicester children’s home.
Janner served in the British army before becoming a lawyer and then an MP. He was a prominent member of Britain’s Jewish community.
His family said he would be “deeply missed” and requested their mourning be respected.