Jean-Sylvain Van de Weyer (19 January 1802 – 23 May 1874) was a Belgian politician, and then the Belgian Minister at the Court of St. James's, effectively the ambassador to the United Kingdom.

Born in Louvain or Leuven, Van de Weyer's family moved to Amsterdam in 1811. The family returned to Leuven when his father, Josse - Alexandre (1769 – 1838), was named police commissioner for the city. Jean - Sylvain studied law at the State University of Louvain and set up as a lawyer in Brussels in 1823. Here he frequently defended newspapers and journalists which fell foul of the government of the United Kingdom of the Netherlands, of which modern Belgium then formed the southern half.

On the outbreak of the Belgian Revolution in 1830, Van de Weyer was in Leuven, but hurried to Brussels where he became a member of the central committee of the Provisional Government of Belgium. His command of the English language resulted in him serving as a diplomatic representative of the revolutionaries. King Leopold I appointed Van de Weyer his "special representative" in London.

Van de Weyer later served as the eighth Prime Minister of Belgium.

He married Elizabeth, only daughter of Joshua Bates of Barings Bank, and formerly of Boston. They had two sons and five daughters, who were brought up in Marylebone and on their country estate at New Lodge in the parish of Winkfield in Berkshire. Their youngest daughter, Eleanor, was the mother of Sylvia Brett, last Ranee of Sarawak. Eldest Son V.W.B Van de Weyer, educated at Eton, Captain of lower boats. Rowed in the winning Eton crew against Radley in Henley .June 26 1858. Prize medals presented by his father.

He was Vice - President of the London Library from 1848 till his death in 1874.