She spoke of the "concern and dismay from the business community", and said the threat of a no deal option was "real" - and "absolutely not" the best option for the UK.
The chancellor is expected to unveil more money for rail links in northern England, known as Northern Powerhouse project, at the Tory conference in Manchester on Monday.
The chancellor used his keynote party conference speech in Manchester to mount a defense of free market economics, which he claimed was coming under assault from Jeremy Corbyn.
Speaking at the conference, the UK Chancellor of the Exchequer Philip Hammond defended capitalism and said that "the process of negotiating our exit from the European Union has created uncertainty so investment has slowed as businesses wait for clarity". Our members, thousands of small businesses across the UK, are united in wanting to see many more young people being trained to higher skill levels. And we will defeat them. This is the Conservative definition of progress and I pledge to the next generation: "we will not let you down".
With Brexit fears putting further pressure on the younger generation, Mrs May said making the United Kingdom a fairer place to live for ordinary working people was a priority.
"And while no-one suggests a market economy is ideal, it is the best system yet designed for making people steadily better off over time and underpinning strong and sustainable public services for everyone. Though robot bricklayers may be a way off yet, we know that, like other sectors, ours will need to innovate and adapt, continuing to develop the traditional skilled trades, while adapting to and incorporating new technologies from low carbon building to greater digitalisation".
But shadow chancellor John McDonnell hit back, saying his opposite number's speech was a waste of everyone's time because he is "clinging to an old economic model that fails the many".
"It was a speech that contained more baseless smears on Labour than Tory policy announcements". Thirty years ago, the Conservatives would have had no problem in countering what Jeremy Corbyn stands for.
The Confederation of British Industry was also unimpressed, with Director-General Carolyn Fairbairn labelling Mr Hammond's address "strong on diagnosis, but weak on action". That is necessary, but not sufficient.
"The UK is facing a generation-defining challenge". A potent cocktail of Brexit uncertainty and dogma-driven politics on both left and right threatens jobs, investment and living standards. "Now is not the time for half measures".