The chancellor has described as “bizarre” and “absurd” accusations he is talking down the economy.
Philip Hammond had been criticised for saying that the Brexit process has created uncertainty.
But in an interview, Mr Hammond said he was a realist and that he wanted to “protect and prepare” the economy for the challenges ahead.
Mr Hammond was speaking in Washington, where he is attending an International Monetary Fund meeting.
The chancellor said: “It is absurd to pretend that the process we are engaged in hasn’t created some uncertainty. But the underlying economy remains robust.
“I am committed to delivering a Brexit deal that works for Britain,” he added.
He refused to answer how he would vote if another referendum was held now. “We’ve had the referendum,” he said. “You know how I voted in it.”
This week, former Conservative Chancellor Nigel Lawson called for Mr Hammond to be sacked, saying he was unhelpful to the Brexit process.
Lord Lawson said: “What he [Mr Hammond] is doing is very close to sabotage”.
Responding to these comments, Mr Hammond said: “Lord Lawson is entitled to his view on this and many other subjects and isn’t afraid to express it, but I think he’s wrong.”
The chancellor, who has been accused of being too pessimistic about Brexit, told the Treasury Committee of MPs this week that a “cloud of uncertainty” over the outcome of negotiations was “acting as a dampener” on the economy.
But speaking on Friday, Mr Hammond said he was optimistic about the UK’s economic future and was in Washington to promote it.
“What I’m doing here in Washington is talking Britain up, talking about Britain’s future as a champion of free trade in the global economy, seeking further moves on liberalisation on trade in services which will hugely benefit our economy.”
He added that Britain had “a very bright future ahead”.
Mr Hammond said the Cabinet was united behind Prime Minister Theresa May’s recent speech in Florence setting out her Brexit plans.
“We know what our proposal is, we put it on the table effectively. Now we want the European Union to engage with it… challenge us… but let’s behave like grown-ups.” he said.
Mr Hammond said the government would not spend taxpayers’ money preparing for a “no-deal” Brexit until the “very last moment”.
He said he would not take money from budgets for other areas such as health or education just to “send a message” to the EU.
One former minister, David Jones, has said billions of pounds should be set aside in November’s Budget for a “no deal” scenario.
He argued that if this did not happen it would be seen as a “a sign of weakness” by EU leaders, who would think the UK was not serious about leaving the EU without a deal.