Portman was elected to Parliament for Shaftesbury in 1852, a seat he held until 1857, and then represented Dorset from 1857 to 1885. In 1888 he succeeded his father and entered the House of Lords.
Estates
At the end of the nineteenth century the 99-year leases on the family properties in London came up for renewal, generating a colossal income for Lord Portman of some £100,000 a year. With this fortune he commissioned Norman Shaw to build a new mansion for him at the family seat in Bryanston, Dorset. Within 30 years, however, it had been sold to Bryanston School, which is still based there. This was because it rapidly became anachronistic and uneconomic even for an aristocratic family to occupy a house on such a scale, and the family was also crippled by death duties when the second Viscount's heir and his heir's heir died within ten years of him.
Family
Son of Edward Portman, 1st Viscount Portman and Lady Emma Lascelles Lord William Henry Berkeley Portman married Mary Selina Charlotte FitzWilliam, daughter of William Charles FitzWilliam, son of the 5th Earl Fitzwilliam, and Lady Selina Charlotte Jenkinson, daughter of the 3rd Earl of Liverpool, on 21 June 1855. They had six sons and two daughters:
The Rt. Hon. Claud Berkeley Portman, 4th Viscount Portman.
Hon. Susan Alice Portman. She married Alan William Heber-Percy, grandson of Bishop Hugh Percy thorugh his son Algernon. They had four sons, and three daughters.
The Rt. Hon. Seymour Berkeley Portman, 6th Viscount Portman.
The Rt. Hon. Gerald Berkeley Portman, 7th Viscount Portman. He married Dorothy Marie Isolde Sheffield, daughter of Sir Robert Sheffield, 5th Baronet. They had two sons, and one daughter, Penolope, who married Brigadier Archer Francis Lawrence Clive, the son of Lt.-Gen. Sir Sidney Clive. They had one son, and daughter.
Two of his sons predeceased him and all four of the others succeeded to his title in the course of time. Lord Portman's first wife died in 1899. In 1908 he married, secondly, shortly before his 79th birthday, Frances Maxwell Buchanan Cuninghame, by whom there were no further children. Lord Portman died in October 1919, aged 90, and was succeeded in his titles by his aforesaid eldest son, Henry Berkeley Portman.
