Mr Williams, the Conservative candidate for the Powys seat he held in the last Parliament under its previous name of Montgomeryshire, is being investigated by the commission for what he described as a “flutter” about the election, due to be held on July 4.
A report in the Guardian on Wednesday said Mr Williams, who is also the Parliamentary Private Secretary to the Prime Minister, made a £100 bet that an election would be held in July.
The report alleges Mr Williams made the bet with Ladbrokes in Montgomeryshire on May 19, three days before Prime Minister Rishi Sunak announced the date of the election outside Downing Street.
Mr Williams released a statement on social media on Wednesday evening admitting he “should have thought through how it looks”.
The statement on his page on X, formerly Twitter, said: “I’ve been contacted by a journalist about Gambling Commission inquiries into one of my accounts and thought it best to be totally transparent.
“I put a flutter on the General Election some weeks ago. This has resulted in some routine inquiries and I confirm I will fully cooperate with these.
“I don’t want it to be a distraction from the campaign. I should have thought through how it looks.”
The Guardian said the bet would have led to a payout of £500 based on 5/1 odds.
A Conservative Party spokesperson said: “We are aware of contact between a Conservative candidate and the Gambling Commission. It is a personal matter for the individual in question.
“As the Gambling Commission is an independent body, it wouldn’t be proper to comment further, until any process is concluded.”
A Gambling Commission spokesman said: “The Gambling Commission does not typically confirm or deny whether any investigations are under way unless or until they are concluded, or if arrests are made or charges are brought during a criminal investigation.
“If someone uses confidential information in order to gain an unfair advantage when betting, this may constitute an offence of cheating under Section 42 of the Gambling Act, which is a criminal offence.“
Mr Williams was approached for comment.