Support for equal marriage has risen substantially in Ireland, and now three quarters of the population would vote yes in a referendum to extend marriage rights to same-sex couples, a new poll suggests.

The Millward Brown poll, commissioned by Marriage Equality Ireland, has shown that the percentage of people in support of equal marriage had risen by 12%, since 2008, and in 2012 was 75%.

In 2008, 63% of Irish people thought equal marriage should be provided to gay couples, and support over the two polls was highest among women, 18-34 year olds, parents and unmarried cohabiting couples.

A constitutional convention is due to discuss the move in April, and Marriage Equality director Moninne Griffith said she was pleased the support for equal marriage was so high.

She told the Irish Times: “We are delighted the constitutional convention has established a date for the issue of providing for marriage equality, and that it is one of the first issues to be considered after this weekend’s meeting.”

“Public support for marriage equality has increased year-on-year. When we began our work in 2006, 51% of people believed same-sex couples should be allowed to marry. That figure has grown 25% in just six years, to a full three-quarters of the population today.”

Figures from the poll suggested that 72% of people said they thought that it was discriminatory to not offer equal marriage rights to gay people, with single people, parents and 25-34 year olds most likely to agree.

It also showed that 90% of 25-34 year olds said they thought gay people should have equal rights, and 88% of parents also thought so.

Two thirds of Irish people felt that Ireland’s reputation as a modern society would be strengthened by allowing marriage equality, and three out of five respondents said they it would promote a more tolerant environment.

The only age-group which showed a majority of opposition to equal marriage was over 65s, which rose from 27% in 2008 to 43% in 2012.

The biggest rise in support for equal marriage came from farmers, which almost doubled from 32% in 2008 to 60% in 2012.

In terms of opinion on gay adoption, 69% of respondents said they thought it was more important for a child to be raised by two loving parents, regardless of gender, than being raised by a mother and father.

The poll also said that 54% agreed that same-sex couples should be legally allowed to jointly adopt a child.

Last week, Ireland’s Equality Tribunal ordered a credit union to pay €24,000 (£20,190) towards an employee as a result of discrimination and victimisation on the basis of their sexual orientation.