The 58-year-old presenter, who was diagnosed with cancer of the oesophagus last year, has been told his treatment for the disease can no longer continue.
During a broadcast on Monday, the father-of-three said doctors have said to “live everyday as it comes” as he had “weeks, possibly months” to live.
Mr Hewlett was due to start his second round of chemotherapy and radiotherapy on Thursday.
Steve Hewlett has been told he may have "weeks to live"
- Rio Ferdinand opens up about his wife's death in BBC documentary
- Tory MP with cancer gets off sick bed to vote for Brexit Bill
It took a little while for it to dawn on me what was really being said. This could be it.
But, after the procedures caused complications with his liver, the treatment can no longer go ahead.
Speaking from the Royal Marsden Hospital in London, Mr Hewlett told fellow Radio 4 broadcaster Eddie Mair: “I’d kind of accepted at some level or other that the outlook was not good for me in the medium to long term.
“Of course you have hope and you do your best and I certainly wasn’t going to give up."
The 58-year-old presenter is now receiving palliative care
“It took a little while for it to dawn on me what was really being said. This could be it. This could be curtains.”
After he received the devastating news, Mr Hewlett decided to marry his long-term partner Rachel in the hospital where he was receiving treatment.
“The whole thing was organised in an hour,” he continued in the moving interview.
The broadcaster is now being cared for by his wife and adult sons
“They got a Chelsea registrar, they got a Chelsea vicar hauled out of a dinner she was in with somebody.
“The nurses managed to produce bunches of flowers, a wedding cake, a couple bottles of Prosecco appeared from goodness knows where and then this ceremony begins."
The Media Show broadcaster is now receiving palliative care, supported by his new wife and three adult sons.
- Sheridan Smith opens up on turmoil of losing her father
- Woman fighting lung cancer: I felt myself dying of fear
- Chas & Dave star Chas Hodges diagnosed with cancer of the oesophagus