Edward Harley , 1689-1741 , 2nd Earl of Oxford Henrietta Cavendish Harley , nee Holles , 1694-1755 , wife of 2nd Earl of Oxford Margaret Cavendish Bentinck , nee Harley , 1715-1785 , wife of 2nd Duke of Portland William Bentinck , 1709-1762 , 2nd Duke of Portland William Henry Cavendish-Bentinck , 1738-1809 , 3rd Duke of Portland William Henry Cavendish-Scott Bentinck , 1768-1854 , 4th Duke of Portland William John Cavendish-Scott Bentinck , 1800-1879 , 5th Duke of Portland Lucy Joan Ellis nee Scott-Bentinck , 1907-1899 , wife of 6th Baron Howard de Walden Frederick George Ellis , 1830-1899 , 7th Baron Howard de Walden Thomas Evelyn Scott-Ellis , 1880-1946 , 8th Baron Howard de Walden General Real Estates Investment and Trust Limited (GREIT) , 1918-1953 Howard de Walden Estates Limited , 1953 - (incorporated in 1963)

Edward Harley , 1689-1741 , 2nd Earl of Oxford Henrietta Cavendish Harley , nee Holles , 1694-1755 , wife of 2nd Earl of Oxford Margaret Cavendish Bentinck , nee Harley , 1715-1785 , wife of 2nd Duke of Portland William Bentinck , 1709-1762 , 2nd Duke of Portland William Henry Cavendish-Bentinck , 1738-1809 , 3rd Duke of Portland William Henry Cavendish-Scott Bentinck , 1768-1854 , 4th Duke of Portland William John Cavendish-Scott Bentinck , 1800-1879 , 5th Duke of Portland Lucy Joan Ellis nee Scott-Bentinck , 1907-1899 , wife of 6th Baron Howard de Walden Frederick George Ellis , 1830-1899 , 7th Baron Howard de Walden Thomas Evelyn Scott-Ellis , 1880-1946 , 8th Baron Howard de Walden General Real Estates Investment and Trust Limited (GREIT) , 1918-1953 Howard de Walden Estates Limited , 1953 - (incorporated in 1963)

The Howard de Walden Estate dates from 1715 when Edward Harley, 2nd Earl of Oxford, began the development of Cavendish Square and the streets around it. This land had previously formed part of the Marylebone Estate of the Dukes of Newcastle. It had passed from Margaret Holles, nee Cavendish, daughter of the 2nd Duke of Newcastle, to her daughter Henrietta Cavendish Harley. At the death of Henrietta's husband, Edward Harley, in 1741, this new Harley Estate passed to his only daughter, Margaret Cavendish Harley, who in 1734 had married William Bentinck, 2nd Duke of Portland. It was subsequently known as the Portland Estate, and was handed down to successive Dukes of Portland. In 1879, the 5th Duke of Portland died without issue and his estates were divided between his sisters, (according to the terms of the 4th Duke's will), and his cousin, who succeeded him as the sixth Duke. The Portland Estate eventually passed to the last surviving sister, Lucy Joan Ellis, who was the widow of the 6th Lord Howard de Walden, and has remained in this family since then.

The Estate's first business trust, General Real Estates Investment and Trust Limited (GREIT), was formed in 1918, changing its name to Howard de Walden Estates Limited (HDWEL) in 1953.
The company was incorporated in its present form in 1963, but the estate is still owned by the family.

During the twentieth century two major portions of the Estate were sold: in 1914 Portland Town, an area east of St John's Wood High Street around 60 acres in extent, and in 1925 another 40 acres, much of it along Oxford Street, south of Cavendish Square and east of Great Portland Street.