A tweet on the official @conservatives channel congratulating Mr Grayling on the appointment was deleted within moments of being sent, but not before it had been shared by a number of Tory MPs and reported on TV.
Theresa May's first major reshuffle since taking office in 2016 was also marked by the unexpected departure of Northern ireland Secretary James Brokenshire, who quit the Government on grounds of ill-health weeks ahead of major surgery for a small lesion to his right lung.
But bigger names were also expected to leave the Cabinet, with Education Secretary Justine Greening, Business Secretary Greg Clark and the Leader of the Commons Andrea Leadsom all reported to be vulnerable as the Prime Minister seeks to assert her authority.
Mrs May's most senior colleagues, including Chancellor Philip Hammond, Foreign Secretary Boris Johnson, Brexit Secretary David Davis and Home Secretary Amber Rudd were all understood to be remaining in post.
Confirming he was leaving Mrs May's top team after almost two years as party chairman, Sir Patrick McLoughlin - who was blamed by many Tories for the party's poor showing in last year's snap election - told Sky News: "I've been in the Cabinet eight years. I have had a very good run and I enjoyed it immensely."
The appointment of Mr Lewis as Sir Patrick's replacement and minister without portfolio was initially overshadowed by the mistaken announcement that Mr Grayling was being moved from Transport Secretary to Conservative chairman.
A Tory source said that CCHQ political director Iain Carter sent the image appearing to confirm Mr Grayling's appointment as chairman to a majority of the party's MPs in a WhatsApp message, before deleting it and saying it was sent in error.
In a major shake-up of CCHQ, the Conservatives announced prominent backbencher James Cleverly as deputy chairman, junior minister Chris Skidmore as vice chairman for policy, Maria Caulfield as vice chair for women, and 2017 intake MPs Kemi Badenoch and Ben Bradley as vice chair for candidates and vice chair for youth respectively.
In a letter to the Prime Minister, Sir Patrick said he felt it was the right time to leave the Cabinet "as we discussed some months ago".
The outgoing chairman has faced criticism over the way the general election campaign was run, but Mrs May said he had responded to the challenge with "vigour" and praised his "wisdom, hard work and dedication".