MPs have been told that passing a law to allow same sex couples to marry will greatly improve the mental wellbeing of young gay people who often contemplate suicide.
A parliamentary select committee is hearing more submissions on the Marriage (Definition of Marriage) Amendment Bill, which MPs will have a conscience vote on.
The Government Administration Committee heard that lesbian, gay, bisexual and transgender young people are eight times more likely to commit suicide than their hetrosexual counterparts.
Counsellor Bill Logan says many of the young people he sees seriously consider suicide because they believe that their sexuality will prevent them being accepted by their peers and their families.
"In just the last year or so I've dealt with four cases of families kicking kids out of their homes with the objective of helping that kid get over their gayness. It always leads to suicidal thoughts. It sometimes leads to suicide."
Mr Logan and other submitters said it is extremely difficult to grow up gay in New Zealand, and changing the law will be an important step in improving the lives of young people.
MPs were also told that making the law change would legitimise gay people in society.
Submitter Andrew Burns told the committee there were only benefits to allowing gay marriage.
"By fully legitimising same-sex relationships at a state level, it legitimises it within the family, the workplace and the schoolyard.
"This can make a significant difference to improving the lives of people who are bullied or harassed for their sexuality."
Mr Burns said New Zealand needs to allow gay marriage as other countries are starting to do.