Many familiar stars of the show are best-known for appearing in the period drama, but plenty of the cast are no strangers to acting in film and TV and enjoyed huge success in their acting work before the first series aired in 2010.
To celebrate their time on screen – we've taken a look back at some of the main cast in their early career...
Dame Maggie Smith
One of the stars of the period drama, Dame Maggie Smith who plays Violet Crawley, Dowager Countess of Grantham, has been a favourite not just on Downton but in plenty of other films and TV shows over the years.
Maggie began working on stage in Shakespearean productions and soon gain attention for her talent. Her first film appearance was in 1956 in Child in the House and also made her Broadway debut in the same year.
She earned her first Oscar nomination in 1965 for her performance in the film adaption of Othello opposite Laurence Olivier, securing her name as one of the greats in the acting world.
Loading the player...
WATCH: The Downton Abbey sequel is in production
Similar to Maggie Smith, Hugh began his acting career working in theatre, but his debut role in film was pretty impressive, too.
He also starred in many films and TV shows in his early career such as The Witches, Richard III and The Bill.
American actress Elizabeth McGovern was trained at the prestigious art school, Julliard, in New York and the year after she graduated in 1981, she received an Academy Award nomination for her role in the film Ragtime.
Elizabeth went on to enjoy plenty more roles including in Once Upon a Time in America alongside Robert De Niro in 1984, and the 1989 film adaptation of The Handmaid's Tale.
Michelle's first TV role came in 2005 in Fingersmith, but she was already an established actress by this point. In 2004, she appeared in the National Theatre's production of His Dark Materials – in which she played Jessie.
Shortly before joining Downton Abbey in 2010, she was nominated for a prestigious Laurence Olivier Award for her performance in the stage show, Burnt by the Sun.
One of Allen's first TV roles was in Ireland's 2004 RTE series Love Is the Drug, for which he was awarded a Best Actor nomination at the Irish Film and Television Awards.
He then went on to appear in HBO show, Rome, a year later, before appearing in The Tudors and films like Rewind and The Sweeney.
Joanne Froggatt is known for her role as Anna Bates in Downton and her other parts in TV shows like Liar, but in early career, she appeared in many beloved shows like Coronation Street, Bad Girls and Dinnerladies.
Laura Carmichael's role in Downton Abbey was her big break and came just two years after she graduated from the Bristol Old Vic Theatre School.
Between 2007 and her joining the show, Laura was working odd jobs and going to various auditions and soon landed the role of Lady Edith Crawley. Go Laura!
Dan began acting in the theatre, working in Shakespearean theatre both in the UK and in the US. His first major acting role in TV came in 2008 when he was cast in the BBC adaptation of Sense and Sensibility, in which he played Edward Ferrars.
Two years later, he was cast as Matthew Crawley in Downton, and the rest, as they say, is history!