Guilherme Valdemar Pereira de Oliveira Martins (Lisbon, 23 September 1952) is a Portuguese lawyer and politician.
He abandoned that party in April 1979, in a division that gave rise to the Independent Social Democrats Action.
In the same year, he was called to perform duties as chief of António Sousa Franco’s Office, who was the Finance Minister of Maria de Lourdes Pintasilgo.
With the Soares’ victory, he was appointed political advisor to the Civil House of the President of the Republic until 1991.
Among other positions he performed, the following may be detached as the representative of Parliament to the Convention on the Future of Europe, secretary general of the Portuguese Committee of the European Cultural Foundation, SEATS president and member of the Board of Directors of Mário Soares’ Foundation.