The ballot was held following current leader Len McCluskey's decision to step down from the role and Ms Graham will take up her new position on Thursday 26 August
Sharon Graham has won the election to be the next general secretary of the Unite union.
Ms Graham won the election after receiving 46,696 votes and will become the union's first female general secretary.
Competitors Steve Turner and Gerard Coyne received 41,833 votes and 35,334 votes respectively.
Releasing a statement confirming the result, Unite said a total of 124,147 votes were cast.
Ms Graham said she is "honoured" to have been elected to the position and understands the "tremendous responsibility" the role brings.
"Our members expect their union to be in their corner so I was proud to stand on a manifesto that pledged to put our members and our workplaces first. I will deliver on those promises," she said in a statement.
"Unite is an incredible force for good in the UK and Ireland but I am fully aware of the huge challenges our members face in the workplace. As general secretary, I will put all the power of our union into defending their jobs, improving their pay and protecting their rights.
"Bad bosses take note. A strong Unite is the best defence that our members can have - my focus now is to build that strength."
The ballot was held following current leader Len McCluskey's decision to step down from the role.
Responding to the result, Mr McCluskey described Ms Graham 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," he said.
"I have been hugely privileged to be at the helm of Unite for the past eleven 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."
He added: "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."
Labour leader Sir Keir Starmer also congratulated Ms Graham on her appointment.
"Congratulations to [Sharon Graham] on her election as general secretary of Unite - the first ever woman to hold that role," Sir Keir posted on social media.
"I'm looking forward to working together to improve the lives of working people across the country."
Ms Graham currently 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 - and during the leadership campaign, described herself as the "workers' candidate".
Unite said Ms Graham will take office on Thursday 26 August.
Following confirmation of the rest, Ms Graham's competitor Steve Turner posted on social media: "With the election now over I want to congratulate Sharon and wish her the very best in her role as general secretary of our great union and thank everyone involved in #TeamSteve for a fantastic, positive, inspiring campaign."
Fellow contestant Gerard Coyne also wished Ms Graham well in her new position.
"Sharon has promised to stop Unite meddling in the Labour Party, to focus on workplace issues and to give members better value for their money. Those are all priorities I have long campaigned for," Mr Coyne said in a statement.
"To achieve them, she will need to open up Unite's £200m annual spending to proper scrutiny and accountability, and engage more of the members in our democracy. This will help drive up turnout in future elections, and that is something all those in our union movement should be fighting for."
Source: Sky News