Erdogan, a pious Muslim, has ruled Turkey as premier since 2003, a period in which he has transformed the country with modernisation projects but also faced accusations of a gradual Islamisation and an erosion of civil rights.
The polls are the first time Turkey will directly elect its president, who has previously been chosen by parliament and in recent decades has fulfilled a largely ceremonial role.
His ruling Justice and Development Party (AKP) has vowed to seek to change the constitution to give the president more powers, which could give Turkey a presidential system similar to France rather than its current parliamentary democracy.
Yet his opponents accuse Erdogan of undermining the secular legacy of Turkey's founding father Mustafa Kemal Ataturk, who based the modern state after the collapse of the Ottoman Empire on a strict separation between religion and politics.
"There really is no uncertainty about this outcome. It's almost a foregone conclusion that Erdogan will win," said Sinan Ulgen of the Carnegie Centre.
While many secular Turks detest Erdogan intensely, he can still count on a huge base of support from religiously conservative middle-income voters particularly in central Turkey and poorer districts of Istanbul who have prospered under his rule.
"We will write the history of the new Turkey on August 10," he told tens of thousands of cheering supporters in Ankara in one of his final election rallies.
Erdogan over three months has spearheaded a lavish and immense campaign that has swamped the efforts of his rivals, holding mass rallies in almost 30 Turkish cities as his face glared on gigantic billboards at pedestrians in Istanbul at almost every street corner.
"National will, national power," reads his main election slogan.