Leading trade unionist Helen Kelly has died after battling lung cancer.

A polarising political figure, she began campaigning for the rights of workers as a child, a battle she fought right until the end of her life.

"I joined the union from the very first job I got. I had a paper run at 10 and I never stopped working," she said.

After working as a teacher, she climbed the ranks of the union movement, following in the footsteps of her father Pat.

In 2007, she became the first woman to lead the Council of Trade Unions, where she battled big business.

She took on the National Government over changes to employment law, and famously, filmmaker Peter Jackson.

NZCTU President Helen Kelly. Source: 1 NEWS

"I hope the movie stays here but that doesn't mean that working people shouldn't be able to negotiate their terms and conditions.

Her work became deeply personal when 29 men were killed at the Pike River mine explosions, and she stood by the families as they fought for tougher health and safety laws.

She did the same for those who lost loved ones on the farms and forest, even opening her home to them.

Last year she married her partner of 12 years Steve Hurring, after being diagnosed with lung cancer,

She had never smoked.

The terminal illness forced her to give up the union's top job, but the battle was far from over, pushing to legalise medical marijuana, and continuing to fight for those killed at Pike River.

She had a son - Dylan - who paid tribute to her skills.

"You can tell that she's a negotiator, I've never won an argument with her in my life."