The new appointment is an attempt by the Palace to improve public understanding of the role and contribution to national life of the Royal Family.
Mr Lewis, 39, who was educated at a north-London comprehensive and at Oxford University, takes up his high-profile appointment in September.
He is being seconded for two years from his present post as corporate affairs director at Centrica plc, the holding company for British Gas.
"It's an honour to be asked to do the job and I hope I can make a contribution. I'm looking forward to starting," he said.
A Labour Party member, Mr Lewis is said to play no active part in party politics.
"Suggestions that he is therefore an active New Labour political figure are totally absurd," said a Palace spokeswoman.
Similarly, the Palace dismissed claims that Mr Lewis would be the Queen's "spin doctor". There's no question of the new position being a spin doctor," said the spokeswoman. "The Communications Secretary will be undertaking a strategic role while working closely with the Press offices at Buckingham Palace and St James's Palace.
"Downing Street have been informed of the appointment but did not participate in the selection process," said the spokeswoman.
The Queen's Press Secretary, Geoff Crawford, will remain in charge of day-to-day handling of the media and will report directly to the Communications Secretary.
Mr Lewis will have direct access to the Queen, Prince Philip and Lord Chamberlain, Lord Camoys, head of the Royal Household.