Sedefkar Mehmed Agha Bicakciu or Sedefqar Mehmeti of Elbasan was the Ottoman architect of the Sultan Ahmed Mosque (the "Blue Mosque") in Istanbul. According to the biographer Cafer Efendi, he was believed to be originating from the city of Elbasan in what is now present day Albania. He went to Istanbul in 1563 (possibly to join the janissary corps). After six years as a cadet (acemioglan) he began the study of music. During a period of twenty years he specialized with inlay in mother-of-pearl, giving him the surname Sedefkar (worker in mother-of-pearl). Later he also switched to architecture. He became a pupil of architect Mimar Sinan, Turkey's most celebrated architect, becoming his first assistant in charge of the office in the absence of Sinan.

In January 1586 he was appointed to complete the Muradiye Mosque in Manisa, a construction started by his master Sinan. He gave a Koran box to sultan Murat III (possibly on the advice of Sinan) and was appointed Gate Keeper (Kapici). When Sinan died in 1588, Mehmed Agha, his first assistant was not appointed as his successor, but instead the Grand Vizier appointed Davut Aga, the Master of the Waterways, as the royal architect. After Davut's execution in 1599, he was succeeded as royal architect by Dalgic Ahmet Aga. In 1606 Mehmed Agha was finally named chief imperial architect to the Ottoman court, succeeding Dalgic Ahmet Aga, builder of the large tomb of Mehmed III in the garden of Hagia Sophia.

From 1609 until 1616 he worked exclusively on the Sultan Ahmed Mosque, called the Blue Mosque because of the colour of its tile work. The design of the mosque was based on the Hagia Sophia (Church of Holy Wisdom).