May is likely to take the opportunity to bring forward some more junior ministers, with Immigration Minister Brandon Lewis and Justice Minister Dominic Raab among those tipped for promotion.
The reshuffle was sparked in part by the resignation of May's ally, Damian Green as the de-facto deputy prime minister, after police who were investigating a separate matter revealed they had found thousands of pornographic images on his computer.
The reshuffle began when the Conservative Party's social media team tweeted congratulations to Transport Secretary Chris Grayling on his appointment as the new Conservative Party chairman.
Ostensibly, she maintains that a reshuffle was made necessary by the spate of resignations late past year of three ministers following separate scandals, including close ally and deputy Prime Minister Damian Green, who was forced to quit over misleading statements he made regarding pornography found on his office computer.More news: Rio Tinto to sell aluminium smelter for $US500m
It is understood that May does not intend to appoint a first secretary of state in what is expected to be her biggest reshuffle since taking office in 2016.
The most senior government ministers - including Foreign Secretary Boris Johnson, Brexit Secretary David Davis, Home Secretary Amber Rudd, and Treasury chief Philip Hammond - all kept their jobs.
Some Conservative lawmakers appeared to agree, with Tory grandee Nicholas Soames tweeting: "I don't mean to be rude or to be seen to be disloyal but there needs to be a major improvement to the reshuffle tomorrow".
But by playing very much to her own party rather than the country, some critics said May risks losing the chance to revitalize what her aides call her "reform agenda", already hampered by Brexit, a scandal over sexual harassment and struggling public services. First Health Secretary Jeremy Hunt, then Education Secretary Justine Greening were locked in discussions with her after rejecting proposed moves.
Johnson, a leading Brexit supporter, kept his job despite challenging Ms May's strategy a year ago.More news: Obama aides return to fight Trump in midterms
After starting the two-year Brexit process in March last year, Britain struck a deal in December on the financial settlement with Brussels, as well as expatriate rights and the Irish border.
Despite winning an important agreement last month from the European Union to move Brexit talks forward from a first phase to a discussion of future trade, May has been criticized at home for her approach to healthcare, housing, transport and Britain's overall Brexit plans.
Pat McFadden MP, leading supporter of pro-EU campaign group Open Britain, said: "The government is implicitly threatening a no-deal scenario".
Ms May was reportedly set to create a new "no-deal" cabinet post on Monday with a responsibility to prepare for a possible breakdown in the talks.
Lidington was also named Chancellor of the Duchy of Lancaster, replacing Patrick McLoughlin, who was sacked as Conservative chairman following criticism of his role in the party's poor performance in last year's snap election.More news: Turkey summons USA diplomat for supporting Syrian Kurd group