Pérez-Llorca was a lawyer by profession and worked in the ministry of foreign affairs.[2] He also worked as a professor of constitutional law at his alma mater, Universidad Complutense.[2] He played a significant role in the creation of Spain's 1978 constitution[2] in that he was part of the seven-member commission, la Ponencia, which produced the draft constitution.[4]
In September 1980, Pérez-Llorca was appointed minister of foreign affairs, replacing Marcelino Oreja in the post.[5][6] The cabinet was headed by Prime Minister Adolfo Suárez.[7] Pérez-Llorca continued to serve as minister of foreign affairs in the next cabinet led by Leopoldo Calvo-Sotelo.[2][7]
Pérez-Llorca's term under Adolfo Suárez was not productive due to the political tensions in the country.[7] In his second term under Leopoldo Calvo-Sotelo the foreign policy of Spain became much closer to the Western countries.[8] In line with this turn Pérez-Llorca focused on the Spain's relations with the European countries.[7] On 17 November 1982 the European Parliament approved the accession of Spain to the European Communities.[7] Another significant event during his tenure was Spain's membership to NATO in May 1982.[7] However, Pérez-Llorca, who feared an Arab oil embargo against Spain, would also prevent Spanish President Leopoldo Calvo Sotelo's consideration to recognize Israel from going forward.[9][10] His term as minister ended in December 1982.[7]
Pérez-Llorca had several positions on the boards of different firms. He co-founded the Pérez-Llorca law firm in 1983 serving as its chairman from then until at least 2005.[11][12] He was the chairman of Urquijo Leasing and AEG Ibérica and a member of the Board of Telefónica and of the Madrid Stock Exchange Council.[11]