Spanish naval officer, was born in Cartagena (Spain) in 1780. On 20 December 1793 he entered the College of Navigation in the Cartagena Comandancia de Pilotos, aged 13, qualifying as a pilotín* on 22 April 1795. He started his career in the Mediterranean, operating with armed launches off Algeciras, Malaga and Cartagena, during which he proved his mettle as a reliable and fearless leader. On 20 May 1796 Guillén joined the frigate Santa Dorotea, but on 10 August he was appointed to the 34 gun frigate Mahonesa. On 13 October 1796 the Mahonesa was captured, between Cabo de Gata and Cartagena, by the 32 gun British frigate Terpsichore, Captain Richard Bowen. Guillén was put ashore at Algeciras and served for some time on look-out duties in the Strait of Gibraltar. On 8 July 1798, he rejoined the frigate Santa Dorotea which was to form part of a squadron of four frigates taking reinforcements and specie to the Algiers garrison. Lieutenant José de San Martín the future 'Libertador' of South America was one of the junior officers on board. On 15 July 1798, the squadron was intercepted by the British 64 gun Lion, Captain Manley Dixon, but after a battle lasting two hours the Dorotea was forced to surrender. Guillén and the other Spanish officers were taken prisoner, but later released on parole, on condition they would not engage in hostilities against England during the war, which Guillén spent teaching mathematics at the Academia de Pilotos in Cartagena. He would never see San Martín again as the two men ended up on different sides during the wars between Spanish loyalists and South American patriots. On 22 January 1805 Guillén was promoted segundo piloto in the Cuerpo de Pilotos, and in 1808 he was appointed, in charge of navigation, to the frigate Proserpina, Capitán de navío José María de Salazar, when she conveyed the viceroy elect of the River Plate from Cádiz to Montevideo.
On 30 August 1809 Guillén was given command of the sumaca * Carlota, with a complement of 46, and at the same time appointed comandante gobernador and ministro de la real hacienda (paymaster of the royal treasury) of the Islas Malvinas, where at Puerto de la Soledad (Port Louis), on 10 January 1810, he relieved Gerardo BONDAS. Guillén brought to the settlement news of the terrible events that had convulsed the Iberian Peninsula, with possible momentous repercussions in the Americas. On his arrival he set out to maintain continuity in government, to sustain the activities in the settlement, and to provide for the maintenance of its installations. He encouraged seal hunting, resulting in reasonable quantities of oil being produced for possible sale in Montevideo. However, the revolution in Buenos Aires on 25 May 1810 caused the overthrow of viceregal government and led to the political separation of Argentina and the Banda Oriental, later to become Uruguay, where the administration had remained for the time being loyal to the crown. In that critical situation the naval authorities in Montevideo had to decide what to do in the Falklands. At the request of Salazar, senior naval officer in Montevideo, a meeting of the Junta Militar Asesora was called by the governor of Montevideo, and held on 8 January 1811. Salazar, a respected organizer, warned that navigational conditions made it imperative for the Junta to decide on an immediate course of action, bearing in mind that to maintain a presence in Puerto de la Soledad would require the despatch of a vessel with 40 or 44 men and 18 months supplies at a total cost of 20,000 pesos. Since there was no money, Salazar proposed withdrawal and so it was decided. That same day Segundo piloto Manuel Moreno, commanding the armed brig Gálvez, was instructed to sail to the Falklands without delay. Because Guillén was junior to Moreno, Salazar instructed him that, while he was to take precedence in all matters relating to the settlement, he was to obey orders from Moreno once at sea.
Acting on the instructions received from Montevideo, Guillén's last official duty as governor at Puerto de la Soledad was to draw up and sign a solemn declaration witnessed and signed by the chaplain of the Carlota and by Moreno. The signatories stated that the coat of arms of Spain had been placed in the bell tower of the chapel and a lead tablet inscribed with the following declaration of sovereignty:
This Island with its harbours, buildings, dependencies and all they contain are the property of the Colony of our Lord Don Fernando 7o legitimate King of Spain and its Indies, and of Soledad de Malvinas.
As a loyalist Guillén remained in command of the Carlota and in the next five years he took part in a number of actions in the River Plate region until he returned to Spain, where the Carlota was paid off in Cádiz on 7 May 1815. By a royal order of 17 April 1812 Guillén had earlier been transferred to the Cuerpo General and promoted alférez de fragata. He continued to serve in the Spanish navy until he died on 12 May 1839 in Cuba in the rank of teniente de navío.