Kate Elizabeth Winslet (/ˈwɪnzlət/ ^ⓘ; born 5 October 1975) is an English actress. Primarily known for her roles as headstrong and complicated women in independent films, particularly period dramas, she has received numerous accolades, including an Academy Award, two Primetime Emmy Awards, five BAFTA Awards and five Golden Globe Awards. Time magazine named Winslet one of the 100 most influential people in the world in 2009 and 2021. She was appointed Commander of the Order of the British Empire (CBE) in 2012.

Winslet studied drama at the Redroofs Theatre School. Her first screen appearance, at age fifteen, was in the British television series Dark Season (1991). She made her film debut playing a teenage murderess in Heavenly Creatures (1994), and went on to win a BAFTA Award for playing Marianne Dashwood in Sense and Sensibility (1995). Global stardom followed with her leading role in James Cameron's epic romance Titanic (1997), which was the highest-grossing film at the time. Winslet then eschewed parts in blockbusters in favour of critically acclaimed period pieces, including Quills (2000) and Iris (2001).

The science fiction romance Eternal Sunshine of the Spotless Mind (2004), in which Winslet was cast against type in a contemporary setting, proved to be a turning point in her career, and she gained further recognition for her performances in Finding Neverland (2004), Little Children (2006), The Holiday (2006), Revolutionary Road (2008), and The Reader (2008). For playing a former Nazi camp guard in the last, she won the BAFTA Award and the Academy Award for Best Actress. Winslet's portrayal of Joanna Hoffman in the biopic Steve Jobs (2015) won her another BAFTA Award, and she received two Primetime Emmy Awards for her performances in the HBO miniseries Mildred Pierce (2011) and Mare of Easttown (2021). In 2022, she produced and starred in the single drama "I Am Ruth", winning two BAFTA TV Awards, and played a supporting role through motion capture in Cameron's top-grossing science fiction film Avatar: The Way of Water.

For her narration of a short story in the audiobook Listen to the Storyteller (1999), Winslet won a Grammy Award. She performed the song "What If" for the soundtrack of her film, Christmas Carol: The Movie (2001). A co-founder of the charity Golden Hat Foundation, which aims to create autism awareness, Winslet has also written a book on the topic. Divorced from film directors Jim Threapleton and Sam Mendes, Winslet has been married to businessman Edward Abel Smith since 2012. She has a child from each marriage, two of whom are the actors Mia Threapleton and Joe Anders.

Kate Elizabeth Winslet was born on 5 October 1975 in Reading, Berkshire, to Sally Ann (née Bridges) and Roger John Winslet. Her mother worked as a nanny and waitress, while her father, a struggling actor, took labouring jobs to support the family. Her maternal grandparents were both actors and ran the Reading Repertory Theatre Company. Winslet has two sisters, Anna and Beth, both of whom are actresses, and a younger brother, Joss. The siblings are of British, Irish, and Swedish descent. The family had limited financial means; they lived on free meal benefits and were supported by a charity, the Actors' Charitable Trust. When Winslet was ten, her father severely injured his foot in a boating accident and found it harder to work, leading to more financial hardships for the family. Winslet has said her parents always made them feel cared for and that they were a supportive family.

Winslet attended St Mary and All Saints' Church of England primary school. Living in a family of actors inspired her to pursue acting from a young age. She and her sisters participated in amateur stage shows at school and at a local youth theatre, named Foundations. When she was five, Winslet made her first stage appearance as Mary in her school's production of the Nativity play. She describes herself as an overweight child who was called "blubber" by her schoolmates and bullied for her appearance. She said she did not let this stop her.

At eleven, Winslet was accepted into the Redroofs Theatre School, an independent school in Maidenhead. The school also functioned as an agency and took students to London to audition for acting jobs. She appeared in a Sugar Puffs commercial and dubbed for foreign films. At school, she was made head girl, took part in productions of Alice's Adventures in Wonderland and The Lion, the Witch and the Wardrobe, and played the lead role of Wendy Darling in Peter Pan. She worked simultaneously with the Starmaker Theatre Company in Reading. She participated in over twenty of their stage productions, but was rarely selected as the lead due to her weight. Nonetheless, she played key roles as Miss Agatha Hannigan in Annie, the Mother Wolf in The Jungle Book, and Lena Marelli in Bugsy Malone.

In 1991, within two weeks of finishing her GCSE examinations, Winslet made her screen debut as one of the main cast members of the BBC science fiction television series Dark Season, written by Russell T Davies. Her part was that of Reet, a schoolgirl who helps her classmates fight against a sinister man distributing free computers to her school. She did not earn much from the job and, at age sixteen, lack of funds forced Winslet to leave Redroofs. To support herself, she worked at a delicatessen.