Gavin Barwell, a former housing minister, replaces joint chiefs of staff Nick Timothy and Fiona Hill.
Publicly and privately the blame game has begun for the Conservatives after failing to win a majority at the general election.
May's attempts to form a government with Northern Ireland's Democratic Unionist Party (DUP) appear to be taking longer than first thought, as Downing Street said Saturday negotiations are ongoing despite an earlier statement that a deal had been reached.
Although Conservatives still hold more seats than any other party, May now must work to build some form of a coalition government in parliament.
"We will welcome any such deal being agreed, as it will provide the stability and certainty the whole country requires as we embark on Brexit and beyond". "The details will be put forward for discussion and agreement at a Cabinet meeting on Monday".
As Mrs May clings on to power, there is disquiet within her party about the link-up with the DUP, which opposes same-sex marriage and abortion.
The prime minister was apparently planning a post-election reshuffle, with Chancellor Philip Hammond and Brexit Secretary David Davis facing the chop.
"I asked for a categoric assurance that if any deal or scoping deal was done with the DUP there would be absolutely no rescission of LGBTI rights in the rest of the United Kingdom, in Great Britain, and that we would use any influence that we had to advance LGBTI rights in Northern Ireland", said the MP, who is a lesbian.
Ms Perrior told the BBC Radio 4 Today programme: 'There was not enough respect shown to people who spent 20 years in office or 20 years getting to the top seat in Government.
After a brief interlude at the British Chambers of Commerce, she returned to work for the Tory party and soon became special adviser to Mrs May at the Home Office, where she teamed up with Mr Timothy.
Advisers and co-leaders of the Prime Minister of Great #britain Nick Timothy and Fiona Hill, who were responsible for preparing the election campaign before the parliamentary elections, resigned because of the loss of the ruling majority by the conservatives.
The lid was lifted on the PM's "poisonous clique" by her former director of communications Katie Perrior.
Writing in The Times she said: "Mrs May condoned their behaviour and turned a blind eye or didn't understand how destructive they both were".
Mr Timothy said he took responsibility for his part in the campaign, including his role in the so-called "dementia tax", which would have seen more people pay for the cost of their social care.
The campaign failed to get "Theresa's positive plan for the future across" or "notice the surge in Labour support".
"One can speculate about the reasons for this, but the simple truth is that Britain is a divided country: many are exhausted of austerity, many remain frustrated about Brexit, and many younger people feel they lack the opportunities enjoyed by their parents" generation... the Conservative Election campaign failed to get this, and Theresa's positive plan for the future, across'.
Oil Falls to Three-Week Low on Rising U.S. Output
He said the nation's oil production was still hovering around 1.5 million barrels per day, down from around 2.2 million bpd. West Texas Intermediate crude futures dropped 26 cents, or 0.54 percent, to $48.1 per barrel.
Crosby scores, Malkin shoots yet Penguins lose 4-1 to Preds
Calle Jarnkrok scored with 5:09 left in the first period , putting the Nashville Predators ahead 1-0 against Pittsburgh. Nashville Predators center and captain Mike Fisher skates during practice Friday, June 2, 2017, in Nashville, Tenn.
WWDC '17: First look at Apple's new iMac Pro
Prices are sticking at US$1,099 for the entry level 21.5-inch iMac , while the top-end 27-inch 5K model stays at $1,799. They also get a pair of USB-C ports, while retaining legacy ports - no repeat of the MacBook Pro dongle debacle.
Google confirms arrival of Chrome browser ad blocker in 2018
This unfavorable user experience could lead users to adopt the ad blocking route to get some relief in their browsing experience. Google will design Chrome's ad blocker to filter out ads that don't meet those guidelines, the company announced on Thursday.
LeBron's brilliance not enough in Game 2 loss to Warriors
Reporter: Well yeah, then you guys are looking at getting swept. "And we're going to need to play better to win on the road". As a result, Sunday evening's Game 2 at Oakland's Oracle Arena registered an even 12 rating between 8:00 p.m. and 11:00 p.m.