The comedy drama, which stars Sally Lindsay and Daniel Ryan, will return later this year.
Sky Living's director Antonia Hurford-Jones said that the show had been "a big hit with viewers".
Nigel Harman, Bobby Ball, George Sampson and Samantha Womack will return for the fourth series, alongside Neil Fitzmaurice, Nicola Millbank and Ainsley Howard.
New cast members include Daniel Ings (Psychoville) and Naomi Bentley (Primeval).
Sky's head of comedy Lucy Lumsden said: "We're very pleased that the much-loved Mount Pleasant will be back for a fourth series later in the year on Sky Living.
"It's been a joy seeing the cast reunited and welcoming some new faces. Fans of the show have a treat in store."