He played a significant role in several key military campaigns, including the battles of Cyprus, Lepanto, Navarino, and Tunis, as well as other expeditions in Italy and Barbary.

For 25 years of service, he was awarded a habit of Santiago and the role as Squadron General and Captain of the São João galleys in the Spanish Armada by King Philip II of Spain.

According to Licentiate Salinas, Diego and his brothers were also descendants of Sancho Fernández de Tejada, renowned knight and general of King Ramiro I of Asturias, who participated at the battle of Clavijo.

[11] Their livestock, which included 15,000 sheep,[12] grazed in those lands, and hundreds of times they walked to the pastures of Extremadura or the royal valley of Alcudia, in La Mancha.

[1] In 1571, Diego de Medrano served as a captain and squadron general in the Holy League and participated in the victorious battle of Lepanto against the Ottoman Empire in the Gulf of Patras.

[15] General Diego de Medrano commanded four Neapolitan galleys, leading a force of 400 sailors and 110 artillery pieces while overseeing 900 enslaved rowers.

[6] In the history of naval warfare, the battle of Lepanto marks the last major engagement in the western world to be fought almost entirely between rowing vessels.

[17] In 1572, Juan de Austria wintered in Naples and received instructions from His Majesty to set out in the spring of 1573 with the fleet to capture Tunis, as the Turks had seized the kingdom from Abu Abdallah Muhammad V al-Hasan, a vassal of the King of Spain.

[1] Captain Diego de Medrano and the Marquess of Santa Cruz reached Tunis, and on their arrival the Turks and Moors there fled, abandoning the city and fortress, allowing the soldiers to secure good quarters and valuable spoils for the night.

[18] In 1576, Captain Diego de Medrano and the Marquess of Santa Cruz embarked with 4,000 soldiers from Zaragoza and headed to Malta to plan a campaign against the Kerkennah Islands.

During the battle, Captain Diego de Medrano was injured, but the forces managed to push the Moors back, securing the island and gaining valuable spoils.

On Sunday the 26th of June, since the weather was in their favor, the Marquess decided to send the twelve galleys ahead under the command of Captain Diego de Medrano.

It seemed reckless to rely on low-lying, long and unstable ships in the face of high waves (...) yet these twelve arrived safely at the island of San Miguel, a thing to admire and celebrate in the hearts of the Spanish.

[27] Diego de Medrano, as the captain of the Capitana and Squadron General of the twelve Spanish Galleys, participated in the war council sessions led by the Marquess of Santa Cruz, where strategic discussions and decisions were made regarding the amphibious assault.

[27] Álvaro de Bazán issued orders establishing rules of conduct for the military discipline of both his soldiers and his naval and land officers during the campaign.

"[27] The galleys assigned to bombard the defenses of the cove of das Molas carried 50-60 arquebusiers and musketeers each, who were responsible for suppressing the defenders and covering the landing.

Medrano's personal Capitana galley, likely one of the four bombarding the fortifications, may have carried additional soldiers due to its larger size and central role in the attack.

The Dominican preacher Brother Hernando del Castillo wrote that, with the union of the kingdoms of Portugal and Castile, Philip II would be "the most powerful lord and king in the world.

"[30] The conquest of Terceira in 1583 and the success of the campaign was not only due to the strength and discipline of the forces but also to the meticulous planning and execution of the landing by Diego de Medrano.

His galleys were crucial in selecting the right landing site, executing a feint towards Plaía, and defending and ensuring the swift consolidation of the beachhead, which were key factors in the overall victory.

The lessons learned from this campaign were so significant that Álvaro de Bazán, from the city of Angra, proposed a similar expedition against England the following year, confident in the abilities of his experienced Captains.

[21] The São João galleys of Portugal in the Spanish Armada appointed to Captain Diego de Medrano were named: Capitana, Princesa, Diana and Bazana.

[6] Before leaving for the English Channel, the Duke of Medina Sidonia, in a dispatch sent to Galicia on 14 June 1588, mentioned his letter to Captain Diego de Medrano.

[6] According to the English, Diana sank near Boulogne, France,[36] however this galley was in A Coruña when Drake and Norreys' fleet attacked in 1589, leading to the myth of María Pita.

[4] Strategic mistakes, particularly the inability to effectively coordinate the Armada with Farnese's Army in Flanders, along with delays that led to unfavorable weather conditions, ultimately doomed the operation.

On 1 September 1552, Charles V, Holy Roman Emperor, issued the Carta Ejecutoria de Hidalguía to confirm the noble status of the Medrano family.

[41][37] From 1579 to 1581, his brother Tomás served on the galleys of Genoa as a Secretary for Prince Giovanni Andrea Doria, Marquis of Torrilla and famous Italian Admiral.

[37] Diego's second brother Francisco Fernández de Medrano was the Lord and Divisero of Regajal, who fought during the French Wars of Religion under Alexander Farnese, Duke of Parma.

[37] His brother Francisco was the ancestor of Diego Fernández de Medrano y Zapata, Lord and Divisero of Regajal, Governor of the Province of Carrión in the valley of Atlixco.

He was also a relative of the famous Captain Gonzálo de Medrano, who fought and died at the great siege of Malta in 1565, while leading his company from Sicily against the Ottoman Turks.