Thanks to the buildings and drawings that he made in his hometown, he was selected for the provincial service. He began to study under the best architects of his time. After three years of education, he successfully attended the "Novice Boys' Club". Sinan's provincial service and his novice boyhood period lasted about nine years. During this time, he had the opportunity to examine Hagia Sophia closely. Sinan learned a lot from self-education, as well as from his devshirme education.
Now it was time to embark on his first expedition as a master architect and master janissary. He participated in the Iran and Egypt expedition of Yavuz Sultan Selim Han as an architect. He attracted the attention of Yavuz Sultan Selim with his successes during the campaign. During his expeditions to Egypt and Iran, he had the opportunity to recognize and examine the architectural structures there.
With Yavuz Sultan Selim leaving his place to Sultan Süleyman Han, a new era started for Mimar Sinan as well. He participated in the Belgrade Campaign organized by Sultan Suleyman Han with the title of Janissary. During this expedition, he built a bridge that allowed soldiers to pass through a swampy area. This success did not go unnoticed by the sultan. After the Belgrade expedition; he participated in Rhodes, Mohac, Irakeyn, Corfu, Pulya and Moldavia Campaigns. Every expedition that he attended, he contributed to the victory of the army and navy. The military expeditions that Sinan participated in, on the one hand, enabled him to advance in the janissary corps, on the other hand, gave the future architect the opportunity to see and get to know the important cities of his age.
During the Iranian campaign, Sinan was declared "Reis-i Mimaran-ı Dergah-ı Âli" (Chief architect) after he built a pier-bridge to allow military galleys to pass to Lake Van. After serving as a Janissary for seventeen years, Mimar Sinan, who was appointed as the "Chief architect", could now begin to perform his works with full competence.