Shortly after midnight on Tuesday 29 May 1453, the final offensive of the Ottomans into Constantinople began. Janissaries attacked first, followed by successive waves of the irregular azaps, who were poorly trained and equipped and Anatolian Turkmen beylik forces who focused on a section of the damaged Blachernae walls in the north-west part of the city. This section of the walls had been built earlier, in the 11th century, and was much weaker. The Turkmen mercenaries managed to breach this section of walls and entered the city but they were just as quickly pushed back by the defenders. Finally, the last wave consisting of elite Janissaries, attacked the city walls. The Genoese general in charge of the defenders on land, Giovanni Giustiniani, was grievously wounded during the attack, and his evacuation from the ramparts caused a panic in the ranks of the defenders.

With Giustiniani's Genoese troops retreating into the city and towards the harbour, Constantine and his men, now left to their own devices, continued to hold their ground against the Janissaries. Constantine's men eventually could not prevent the Ottomans from entering the city and the defenders were overwhelmed at several points along the wall. Janissaries, led by Ulubatlı Hasan, pressed forward. Many Greek soldiers ran back home to protect their families, the Venetians retreated to their ships and a few of the Genoese escaped to Galata. The rest surrendered or committed suicide by jumping off the city walls. Constantinople was finally conquered and the childhood dream of Mehmed II was achieved.