He says he believes his daughter is "tossing away" her royal duties "for money".
Markle Snr even went on to admit he is “ashamed” of his daughter.
"When they got married they took on an obligation, and the obligation is to be part of the Royals and to represent the Royals. And it would be foolish for them not to,” the 75-year-old said.
"They are turning it [the Royal Family] into a Walmart with a crown on...This is not the girl I raised," he continued.
"This is one of the greatest long-living institutions ever. They are destroying it, they are cheapening it, making it shabby…they shouldn't be doing this.
"I think both of them are turning into lost souls at this point,” he concluded.
Thomas’ shock attack against his daughter comes just 24 hours after Buckingham Palace released a statement confirming that Harry and Meghan will relinquish their royal titles and lose public funding after they made the decision earlier this month to step down as senior royals.
“Following many months of conversations and more recent discussions, I am pleased that together we have found a constructive and supportive way forward for my grandson and his family,” Her Majesty revealed in her statement on Saturday.
“Harry, Meghan and Archie will always be much loved members of my family. I recognise the challenges they have experienced as a result of intense scrutiny over the last two years and support their wish for a more independent life. I want to thank them for all their dedicated work across this country, the Commonwealth and beyond, and am particularly proud of how Meghan has so quickly become one of the family,” the statement continued.
“It is my whole family’s hope that today’s agreement allows them to start building a happy and peaceful new life.”
The Palace also confirmed that the new arrangements will take effect in spring 2020.
As a result of the changes the pair will be known as Harry, Duke of Sussex and Meghan, Duchess of Sussex.
The agreement will also see the pair repay $A4.5 million in taxpayers' money that was spent renovating their Windsor home, Frogmore Cottage.