Jeremy Corbyn has unveiled what he called a "unifying" new shadow cabinet, naming his left-wing ally John McDonnell as shadow chancellor.
Defeated leadership rival Andy Burnham is shadow home secretary, while Hilary Benn remains shadow foreign secretary.
The most senior roles on the Labour front bench are all taken by men, leading to criticism from some MPs.
But half of the total posts went to women, including shadow defence, education, business and health.
Within a very short time it's become clear that the nature of the post-leadership election Labour team will mean policy shifts which soon make themselves felt in London.
The appointment of John McDonnell as shadow chancellor will do more than send tremors through the City.
It signals an immediate change in Labour policy towards aviation, guaranteeing a stance firmly opposed to a third runway at Heathrow.
The party had previously broadly accepted the independent Davies commission's recommendations of expansion at Heathrow, subject to conditions on noise and air pollution being met.
But Mr McDonnell, MP for Hayes and Harlington, is the most strident opponent of any further expansion - with a long history of protest.
A senior union leader had said "the jury is still out" on whether a Jeremy Corbyn-led Labour Party will be able to "reach out" to the public.
GMB boss Sir Paul Kenny said Mr Corbyn should be judged by how Labour did in elections and not by the enthusiasm shown by many Labour activists to him.
"The rallies are not enough... to say people will rush to Labour," he said.
Mr Corbyn has completed his new shadow cabinet, saying it is a "great" team, drawing on all sections of the party.
After his resounding victory on Saturday, Mr Corbyn has named a 31-strong shadow ministerial team, appointing close ally and fellow left-wing MP John McDonnell as shadow chancellor and giving key jobs to Andy Burnham, Hilary Benn, Heidi Alexander and Lucy Powell.
Unlike other leading unions, which backed Mr Corbyn, the GMB did not endorse any candidate.
And speaking to BBC Radio 4's World At One from the TUC Congress in Brighton, Sir Paul refused to be drawn about Mr Corbyn's long-term prospects, saying it was too early to say whether he would lead the party into the next election.
He likened the new shadow cabinet to "a train of very, very many carriages".
He added: "I don't think the rallies themselves, as enthusiastic as the support was, at this stage is enough for me to say, 'Well I think wherever we go in the country, people will flock to Labour.'
"Let's see how we get on, let's see the real tests, let's see how the public react and let's see how effectively when the tests come, whether they are by-elections, or local government elections or indeed the elections of mayor in London next year.
"Lets see what the voters say. Because at the end of the day, they are really the important ones."
These comments were reinforced by the TUC's general secretary, Frances O'Grady, in her speech to the annual congress.
She warned Labour it must "appeal to the country at large" and aim to win the next election, urging Mr Corbyn and his colleagues to "look sharp, pull together... and get stuck in and oppose".
Labour leader Jeremy Corbyn has told the BBC that he will not campaign for Britain to leave the European Union.
Mr Corbyn said that while policy was "developing" he could not foresee a situation where Labour would campaign for a "Brexit" under his leadership.
He has come under growing pressure from Labour MPs to clarify his position.
Wouldn't leaving the EU give him more of a blank cheque?