She worked for a time as apprentice to a sempstress, until she attracted George Farquhar's attention by reciting some lines from a play in his hearing. She thereupon obtained an engagement at Drury Lane, where her beauty rather than her ability slowly brought her into favour, and it was not until ten years later that she was generally acknowledged as the best actress of her time.
In polite comedy, especially, she was unrivalled, and even the usually grudging Colley Cibber acknowledged that she had as much as he to do with the success of his The Careless Husband (1704), in which she created the part of Lady Modish, reluctantly given to her because Susanna Verbruggen was ill. Of her portrayal of Lady Townly his The Provok'd Husband (1728), Cibber was to say, memorably, "that here she outdid her usual Outdoing." She also played the title role in Ben Jonson's Epicoene, and Celia in his Volpone. In tragedy, too, she won laurels, and the list of her parts, many of them original, is a long and varied one.
She was the theatrical idol of her day. Her exquisite acting and lady-like carriage were the delight of her contemporaries, and her beauty and generosity found innumerable eulogists, as well as sneering detractors. Alexander Pope, in his Sober Advice from Horace, wrote of her "Engaging Oldfield, who, with grace and ease, Could join the arts to ruin and to please." It was to her that he alluded as the lady who detested being buried in woollen, who said to her maid "No, let a charming chintz and Brussels lace Wrap my cold limbs and shade my lifeless face; One would not, sure, be frightful when one's dead, And Betty give this cheek a little red."
Oldfield was forty-seven when she died on 23 October 1730. She divided her property, for that time a large one, between her natural sons, the first by Arthur Mainwaring (1668-1712) who had left her and his son half his fortune on his death and the second by Lieut.-General Charles Churchill (d. 1745). Mrs Oldfield was buried in Westminster Abbey, beneath the monument to Congreve, but when Churchill applied for permission to erect a monument there to her memory the dean of Westminster refused it.