Sharon Graham has vowed to lead “a relentless fight for jobs, pay and conditions” after winning the election to be the next general secretary of Unite after receiving almost 5,000 more votes than her nearest rival.

She said the union should “get back to the workplace”, after she received 46,696 votes, with 41,833 for Steve Turner and 35,334 for Gerard Coyne.

Ms Graham will take over from Len McCluskey, becoming the first female leader of Unite, one the country’s most powerful trade unions.

Labour leader Sir Keir Starmer tweeted his congratulations, writing: “I’m looking forward to working together to improve the lives of working people across the country.”

Ms Graham leads Unite’s Organising and Leverage Department, which specialises in taking on hostile employers.

She has led recent disputes at British Airways and Crossrail as well as campaigning to unionise Amazon.

She described herself as the “workers’ candidate”, pledging to take Unite “back to the workplace”.

She has said she wants to rebuild the union as a movement which delivers industrially and politically.

Following the announcement of her victory, she said: “It is an enormous privilege for me to have been elected as the general secretary of Unite.

“Unite members across the UK and Ireland, have spoken. They want change. They have rallied in their tens of thousands to our demand that Unite should get back to the workplace and deliver what it says on the trade union tin – a relentless fight for jobs, pay and conditions.

“I stand for a fight against the gross injustices that blight the lives of our members, and British society as a whole.

“What is happening to workers all over Britain in the cascade of ‘fire and rehire’ threats being issued by rogue employers is only one recent example of these injustices. I will make sure that the union fights this with all its power in the future.

“We won the election because of the votes of the fearless who came behind our banner. We won because of the army of volunteers in my campaign who stood against the stream and, month after long month, battled to deliver our vote. The trade union movement is nothing if it is not a crusade.

“Our crusade has won and I will be eternally grateful to all those who made that possible, and make no mistake, the pledges I have made to every member will be made real.”

Mr McCluskey said: “I thoroughly congratulate Sharon on her victory, which reaffirms her as the most formidable campaigning force in our movement.

“It’s a fantastic achievement and I am very proud to be handing over to our first woman general secretary.

“I have been hugely privileged to be at the helm of Unite for the past 11 years. Sharon has been a valued and close friend, an integral part of my senior team throughout my time in office so I know from experience that she is a talented, dedicated and passionate trade unionist.

“I have every faith that she will run our union in a manner true to its fighting-back spirit.

“Sharon comes into office at a time of great uncertainty for our members and a challenging political environment.

“From assaults on workers’ rights to the fear that the end of furlough will bring with it increased and needless unemployment, the in-tray is full.

“But I know that she will build on our values and harness the talents of our great union in the service of our members and our movement.”