Winslet, who also stars in the film, directs from a screenplay by her son Joe Anders. The story was partly inspired by their personal experience of losing Winslet's mother, Anders' grandmother, to cancer in 2017.
"I just wanted to make a film that felt authentic and real," said Winslet, premiering the movie with Anders and the cast in London.
"I also didn't want to make a story that was about someone who dies because it's really not. It's actually about the life that is given to the people who are left behind."
Winslet said she wanted to set the movie in Britain's National Health Service space because it is "massively undervalued".
"And we need to give credit and honour the people who do that incredible work, especially our palliative care workers," she said.
"It's entirely fictional," added Anders. "I think it just emotionally came from that place of sending my grandmother off."
Anders, whose father is filmmaker Sam Mendes, wrote the script when he was 19, and showed it to Winslet for feedback.
"I didn't even know if I could write a screenplay. I just really wanted to give it my best shot. And the fact that it's been made into a movie is insane," Anders, now 21, said.
Winslet, who has three children, said she had thought about stepping behind the camera over the years but raising a family kept her busy.
"There just wouldn't have been that space in my life, I think, emotionally and just energetically. I couldn't possibly have added anything else into the juggle of it all. But this felt like the right moment, and I felt really ready to do it," she said.
In the film, family matriarch June (Helen Mirren) is hospitalised shortly before Christmas. Her husband (Timothy Spall), son (Johnny Flynn) and three daughters, played by Winslet, Andrea Riseborough and Toni Collette, and their offspring rush to her bedside, bringing with them conflict and personal struggles, but also joy and care.
"It's such an honest look at the transition from life into the next. And it's about family, the mess and the beauty of the dysfunctional family system," Collette said.
Goodbye June is released in select UK cinemas on December 12 and starts streaming on Netflix on December 24.
33°C