Thomas Markleis in intensive care after undergoing emergency surgery, his son has said.
The Duchess of Sussex's father was rushed to hospital on Tuesday after he was taken gravely ill at his home in the Philippines.
He was in an intensive care unit on Wednesday night after undergoing three hours of surgery earlier in the day.
Mr Markle will need to undergo a second operation to remove a blood clot.
"I took dad to a hospital close to our home and they did various scans and the doctors said his life was in imminent danger," his son Thomas Jnr told the Daily Mail.
"They raced us by ambulance, with the sirens going, to a much bigger hospital in the centre of the city. My dad has undergone emergency surgery. I would ask everyone around the world to keep him in their thoughts."
Mr Markle, who has beenestranged from his daughtersince her wedding to the Duke of Sussex in 2018, has been in poor health for several years.
He said his daughter was furious with him when heposed for paparazzi pictureson the eve of her wedding and previously said his "only wish is to see my grandchildren before I die".
He suffered two heart attacks just before Meghan's wedding at St George's Chapel, Windsor Castle, whichprevented him from flyingfrom Los Angeles to London to be by his daughter's side. The King ended up walking Meghan down the aisle.
Mr Markle later suffered a stroke in 2022 which left him unable to speak for months.
His son said he hoped Meghan, who released theChristmas special of her Netflix showearlier on Wednesday, shows her father "some compassion".
"He is literally fighting for his life," Thomas Jnr added.
Mr Markle's daughter Samantha, 61, said she believed the strain of the past few years had taken its toll on her father and made him more fragile.
"He is a strong man, but he has been through so much. I am praying that he is strong enough to survive this," she said."My father has been through two heart attacks, a stroke and an earthquake. I hope he can pull through this."
The Telegraph has approached The Duchess of Sussex's representatives for comment.
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