Stella Assange said the WikiLeaks founder was told he was being moved to a bare cell “for his own protection”.
He had no visits over the weekend following home secretary Priti Patel’s announcement on Friday that she was allowing his extradition to the United States.
“Prison is a constant humiliation but what happened on Friday felt especially cruel,” said Ms Assange.
“After the announcement of Patel’s decision, Julian was taken from his cell so that he could be strip searched, and then escorted to a bare cell where he remained for the rest of the weekend.
“His own cell was searched. They were looking for things that could be used to take one’s own life.
“In the bare cell, guards logged his status every hour until he was allowed to return to his cell on Tuesday.
“This kind of thing never becomes more tolerable. Any person would find it degrading. The mental strain on Julian is enormous as it is, having to process what is essentially a death sentence.
“The fact he is imprisoned while this outrageous extradition proceeds is a grave injustice in itself. He needs to deal with all that, while preparing for a complex appeal to the High Court.”
Ms Assange has previously claimed her husband is “certain” to die in US custody if he is extradited to America, warning that the WikiLeaks founder’s health is deteriorating.
On the day the British government announced it was ordering the extradition of the 50-year-old to face charges of spying and trying to gain access to a Pentagon computer, Ms Assange told The Independent she feared deeply for his wellbeing.
She said the fight to prevent his transfer from London to Washington DC would continue – Mr Assange has 14 days to appeal – but said she worried about the strain he was under.
John Rees, a leading member of the campaign for Mr Assange to be freed, said: “This is simply extrajudicial punishment.
“It’s unacceptable and it’s surely illegal. But it shows how much pressure the authorities are under to free Assange that they behave this vindictively.
“We need to redouble our efforts to stop the extradition, for Julian Assange’s sake and for the defence of a free press.”
Mr Assange, an Australian citizen, was arrested in April 2019 having spent five years in the Ecuadorian embassy in London after he sought political asylum.
He fought extradition to Sweden, where police said they wanted to investigate him over two accusations of sexual assault. Mr Assange has denied the claims and said he believed he would be taken to the US.
The US claims he put people’s lives at risk as a result of the material he published on WikiLeaks, some of which was provided by former army intelligence officer Chelsea Manning.
Ms Manning was convicted in 2013 of the largest leak of classified documents in US history and sentenced to 35 years in prison. In 2017, US president Barack Obama commuted her sentence to time served and she was released from a military prison in Kansas.
Mr Assange married his long-term partner inside high-security HMP Belmarsh in southeast London during visiting hours in March.
Supporters said the couple were allowed six guests, including Mr Assange’s two brothers and his biological father John Shipton.
The newlyweds met in 2011 when Ms Assange, then Stella Moris, joined Mr Assange’s legal team. The couple have two children together.
Additional reporting by Press Association