The Prime Minister received a boost on Wednesday ahead of exit negotiations and for an election she is seeking to cast as a vote on Brexit, with US House of Representatives speaker Paul Ryan saying America stands ready to strike a free trade deal with the United Kingdom as soon as possible.
May wasted no time, going from the vote in Parliament to kick off her campaign with a speech in to supporters northwestern England.
David Dimbleby, who hosted the BBC leaders' debates in both 2010 and 2015, said a refusal to take part in TV showdowns with her rivals could be "rather perilous" for May.
Critics of an early election accuse May of taking advantage of low ratings for the main opposition Labour Party.
Britain's next election had been scheduled for May 2020, but a two-thirds majority in parliament could overrule that in Wednesday's vote, which British media reported could come at around 1300 GMT after an hour and a half of debate.
Khan said, "I will be fighting hard for every Labour vote over the coming weeks - a Labour government is in the best interests of all Londoners and the whole country".
Now that lawmakers have approved the election, Parliament will be dissolved at midnight on May 2, 25 working days before election day.
The SNP, whose MPs abstained in Wednesday's vote, has accused Mrs May of political opportunism and said only it stands in the way of a "hard-line" Tory government.
"A Prime Minister who can not be trusted", said Labour Leader Jeremy Corbyn.
Despite Corbyn's bravado, his party is demoralized and divided under his left-wing leadership and is expected to fare badly.
While Ms. May herself has scored well in polling compared to Mr. Corbyn (a poll last week put her 37 points ahead), other data suggest a level of support for the Labour leader's policies - including a recent poll by ComRes for The Independent newspaper that found support for raising the minimum wage, and the top rate of tax, and charging a goods and services tax on private schools as Mr. Corbyn has suggested.
She said she also understood that Mr Corbyn had ruled out "progressive alliances" with other parties, such as the Greens, as a way of thwarting Conservative attempts to increase their majority.
"It's the right decision, it's in the national interest, and that's what this election is about". May reiterated her reasons for holding an election, insisting that political divisions in Westminster risked weakening Britain's hand in the negotiations with Europe.
"Brexit isn't just about the letter that says we want to leave".
Mrs May added: "I believe in campaigns where politicians actually get out and about and meet with voters".
That could narrow her negotiating options - and puncture investors' hopes for a softer Brexit just as quickly as calling the election has raised them. Leaders of European Union states are due to adopt negotiating guidelines at an April 29 summit, and the bloc will prepare detailed plans for the talks with Britain by late May.
"Following their conversation, the president considers that the real political negotiations on Article 50 with the United Kingdom will start after the elections foreseen for the 8th of June", the spokesman said, referring to the European Union treaty rule that regulates the exit of a member state from the bloc. The premier has already backed out from televised debates, drawing fire from opposition leader Jeremy Corbyn.
And Plaid Cymru leader Leanne Wood - whose profile received a major boost from her involvement in two of the 2015 broadcasts - said: "Theresa May should be empty chaired if she doesn't show up to any planned TV debates".