Mary Constance Charteris, Countess of Wemyss and March (née Wyndham; 3 August 1862 – 29 April 1937), styled Lady Elcho from 1883 to 1914, was an English society hostess and an original member of The Souls, an exclusive social and intellectual group.

Mary Constance Wyndham was born on 3 August 1862 in London at her parents' home in Belgrave Square.

[1] She was the eldest daughter of Percy Wyndham and Madeline Caroline Frances Eden Campbell.

[2] Wyndham and her siblings and their spouses were members of The Souls, an elite English social group.

[4] Her life was detailed in the book Those Wild Wyndhams by Claudia Renton.