Recognised for her starring role in the mini-series, Kate was warmly congratulated by Hugh Laurie and her co-star Guy Pearce.
Honoured in the supporting actor category himself, he joked: "I got to have sex with Kate Winslet many many times."
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The drama centres on a young mother with a talent for baking, who is forced to hunt for work to support herself and her two young daughters, after throwing her husband out of the house.
Dressed in a glamorous red gown, emotional Kate, who had a tough year in 2010 with the break up of her marriage, dedicated the award to her mother.
"Mildred Pierce was capable of great acts of love as a mother.
"It doesn't matter how old you are or what you do with your life, you will never stop needing your mum.
"And I will never stop needing mine, so thanks mum."
Meanwhile ITV1's hit period drama Downton Abbey picked up four gongs, including best mini-series and a best supporting actress award for Dame Maggie Smith.
Downton, which launched its second series in the UK on Sunday night, was also honoured for its writing and directing, with gongs for Julian Fellowes and Brian Percival.
Julian called the success of the show a "David and Goliath story", and said: "I would like to thank you, the American industry.
"Ten years ago you kick-started my second career with an Oscar, tonight you have nurtured it."
The 63rd Primetime Emmys ceremony in Los Angeles also saw Mad Men win its fourth consecutive best drama series award, while Modern Family claimed its second best comedy trophy.
Other notable wins included Martin Scorsese, who was honoured for directing drama series Boardwalk Empire and Julianna Margulies, named best lead actress in a drama series for The Good Wife.
Emmy Awards: The night's big winners
- Outstanding supporting actress in a comedy series: Julie Bowen as Clare Dunphy in Modern Family
- Outstanding supporting actor in a comedy series: Ty Burrell as Phil Dunphy in Modern Family
- Outstanding lead actor in a comedy series: Jim Parsons as Sheldon Cooper in The Big Bang Theory
- Outstanding lead actress in a comedy series: Melissa McCarthy as Molly Flynn in Mike & Molly
- Outstanding supporting actress in a drama series: Margo Martindale as Mags Bennett in Justified
- Outstanding supporting actor in a drama series: Peter Dinklage as Tyrion Lannister in Game of Thrones
- Outstanding lead actress in a drama series: Julianna Margulies as Alicia Florrick in The Good Wife
- Outstanding lead actor in a drama series: Kyle Chandler as Coach Eric Taylor in Friday Night Lights
- Outstanding supporting actress in a miniseries or movie: Maggie Smith as Violet, Dowager Countess of Grantham in Downton Abbey
- Outstanding supporting actor in a miniseries or movie: Guy Pearce as Monty Beragon in Mildred Pearce
- Outstanding lead actress in a miniseries or movie: Kate Winslet as Mildred Pearce in Mildred Pearce
- Outstanding lead actor in a miniseries or movie: Barry Pepper as Bobby Kennedy in The Kennedys
- Outstanding miniseries or movie: Downton Abbey
- Outstanding drama series: Mad Men
- Outstanding comedy series: Modern Family