Shadow chancellor and republican, John McDonnell, will not be expected to kneel before the Queen when he joins the Privy Council, his spokesman said.
Mr McDonnell will be entitled to be referred to as 'Right Honourable' and receive top secret national security briefings on becoming a member.
But the spokesman said it would not be a snub to the monarch if the shadow chancellor opts to shake the Queen's hand, rather than kneel before her when he joins the select grouping of senior advisers.
"There are no specific ceremonial requirements we have been informed of, but as John has said, he will adhere to any procedures asked of him as being a member of the Privy Council," he added.
Tory former Cabinet minister Norman Tebbit, who was wounded in the 1984 bombing of the Grand Hotel in Brighton, disapproved of the move given that Mr McDonnell had to apologise for saying that IRA members deserved to be "honoured", and that he would like to go back in time and kill Margaret Thatcher.
"His comments about the IRA, the Royal Family, and wanting to assassinate Margaret Thatcher should all disqualify him from the position," Lord Tebbit told the Daily Mail.
Downing Street announced the appointment, stating: "The Queen has been pleased to approve that John McDonnell MP be sworn of Her Majesty's most Honourable Privy Council."
The Privy Council is mainly composed of senior politicians, but includes some bishops and judges, and has advised the monarch since the Norman era.
Buckingham Palace declined to comment.
Labour leader, and fellow republican, Jeremy Corbyn said after he joined the Privy Council last year: "We shook hands like two adults", when asked if he had knelt before the Queen.