Magda Szubanski has broken down in tears on Andrew Denton's Interview while discussing what she described as the toughest year of her life.

The interview, which was filmed earlier this month, saw Szubanski open up about what it was like to lose her mother just weeks out from the announcement that the Australian public had voted in favour of same-sex marriage.

The Kath and Kim star was the public face of the marriage equality campaign and admitted that meant she hasn't had time to properly process her mother's death.

"It's been... the toughest year of my life without question," she told Denton. "Mostly because of mum. But the marriage equality stuff was something I was proud to do. I just felt so nervous the whole time because if I put a foot wrong, I could be blowing it for everyone. I haven't had a proper break since that."