Labour have appointed their second-ever female general secretary in the party's history as trade unionist Jennie Formby took on the top role.
The Unite employee was made Labour's most senior official on Tuesday to boost Jeremy Corbyn's influence over the party's internal machinery.
Ms Formby was appointed by Labour's ruling National Executive Committee (NEC) to replace outgoing general secretary Iain McNicol, who announced his resignation last month.
She will now have responsibility for recruiting party staff, overseeing campaigns, organising annual conferences, and guarding Labour's legal and constitutional structures.
Ms Formby was supported by shadow chancellor John McDonnell and was also seen as the pick of Mr Corbyn.
With the Labour leader's left-leaning supporters having also recently secured a majority on the NEC, Ms Formby's appointment will be viewed as Mr Corbyn's allies strengthening their control over Labour.
Mr McNicol's departure was accompanied by reports he was forced out of the position, having been unpopular with Mr Corbyn's supporters.
Outside the NEC's meeting on Tuesday, at which they decided Ms Formby's appointment, a group of Corbyn-supporting Momentum activists were reported to have formed a picket and chanted: "McNicol's gone, now it's time for the rest of them".
The reports prompted condemnation from Labour MPs and trade union bosses, with UNISON general secretary Dave Prentis posting on Twitter: "A depressing and shameful day when some think it's ok to treat @uklabour staff and fellow trade unionists like this."
Ms Formby, who has sat on the NEC for seven years, described herself as "honoured" to be appointed Labour's new general secretary.
"Last year's General Election showed the strength of our movement when we are united, challenging this Government's failed and damaging policies and campaigning for real change, in the interests of communities across the UK," she said.
"Labour is preparing for government and I look forward to working with Jeremy Corbyn, our party's staff, Members of Parliament, members and affiliates to oppose the Conservatives' destructive austerity programme inside and outside Parliament, and to win elections to build a society that works for the many, not the few."
Mr Corbyn said: "I would like to congratulate Jennie Formby on her new role as general secretary of our party.
"Her talent, experience and commitment to the Labour and Trade Union movement makes me confident she will play a crucial role in building on last year's inspiring General Election advance and taking our party forward to victory.
"The Labour Party is on the cusp of power and we are ready for a General Election whenever it comes.
"We have the team, the passion and the policies to win the support of the British people, form a government and transform our society for the many, not the few."
Richard Angell, director of Progress, the pressure group of so-called "centrist" Labour members, offered Ms Formby a "to-do list" with a focus on putting Mr Corbyn in Downing Street, boosting Labour's position in opinion polls, implementing an independent sexual harassment and anti-bullying policy, and dealing "promptly" with anti-Semitism cases.
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He said: "The new establishment has a new leading member. Not every Labour leader gets their choice of general secretary, especially not their first choice, but Jeremy Corbyn has.
"For the sake of the Labour Party and the voters that rely on us, we wish Jennie Formby well in the role."