The court found Terranova Homes' 106 female and four male caregivers were all paid between $13.75 and $15 an hour.
The minimum wage is currently $13.75 an hour.
The court also found the defendant could not prove it paid its four male caregiver employees the same as its 106 female caregivers, or that it would pay replacement males the same rates.
Mr Ryall said the next stage in the case was for the court to get evidence about what the comparative pay rates would be if the industry was male-dominated.
"We need to establish that given the skills and experience and effort required in this work, what is the equivalent male comparator?
"The court has found that some industries and some workplaces are low-pay ghettos because the nature of the work is intensively female and therefore the skills of that work has been devalued ... and that's certainly the case with caregiving."
Mr Ryall said the outcome was the greatest advance for the rights of working women since the passing of the Equal Pay Act in 1972 and would be celebrated by caregivers and other low-paid women workers throughout New Zealand.
"The court has recognised that caregivers are paid abysmally low pay rates because they are women and has dismissed Business New Zealand arguments about the cost of removing pay discrimination as akin to the economic arguments against removing slavery."
Mr Ryall said the union wanted to see a fair rate set for all caregivers.
The Public Service Association (PSA) says the decision has far-reaching implications for thousands of women who work in low paid occupational groups.
PSA national secretary Brenda Pilott said it was a big step in terms of getting rid of the notion of 'women's work' and reinforced the fact that equal pay was a basic human right.
New Zealand Nurses Organisation industrial adviser David Wait said with a 93 per cent female membership, the decision was important for the organisation.
"Today is a great day for each and every one of them. Equality is now one step closer."
