"Protection of secularism is one of my basic principles. Nobody should worry about this," Gul said, adding that he would be a president for all Turks.
His first attempt to become president in April plunged Turkey into a political crisis.
An opposition boycott blocked the presidential vote in parliament and the military threatened to intervene to protect the secular system.
And the leaders of the opposition Republican People's Party (CHP), the second biggest in parliament after the AK Party, said they would again boycott presidential elections
It may be that the Turkish military feels a little bit weaker after the AK Party's election victory.
Al Jazeera's Barnaby Phillips |
The party also threatened to boycott receptions and foreign trips if Gul was elected.
Mustafa Ozyurek, the CHP's Deputy Chairman, said: "Gul's speeches and writings in recent past show that he does not agree with the basic values of the republic."
April's turmoil prompted early legislative elections on July 22, in which the AKP won a landslide victory and a second five-year mandate.
The AKP, which holds 341 seats in the 550-member parliament, is virtually certain to elect Gul in the third round of voting when the winner needs a simple majority of 276.
'Loss of face'
The foreign minister said one of his main goals would be to facilitate Turkish entry into the European Union.
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Huge protests have taken place against
Gul's candidacy [AFP]
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"EU membership is all governments' goal, I will help the government in reaching this target," he said.
Gul said earlier on Tuesday he had won the backing of colleagues in the ruling Justice and Development (AK) Party.
He has said the AKP's recent victory is a popular vindication of his presidential ambitions.
The AKP, whose roots lie in political Islam, describes itself as a conservative, pro-Western party.
Secularist Turks and the main opposition Republican People's Party (CHP) are hostile to Gul's bid arguing that his presidency would undermine the country's secular system.
In April the military threatened to take action to protect the secular system.
Al Jazeera's Barnaby Phillips in Istanbul says it would amount to an enormous loss of face for the Turkish military if Mr Gul's presidency floated through.
"It may be that the Turkish military feels a little bit weaker after the AK Party's election victory," he said.
Opposition talks
Gul held talks with Devlet Bahceli, the leader of the far-right Nationalist Movement Party (MHP), describing them as "beneficial and fruitful."
"I explained to them how I will act if parliament elects me as president," he said.
Gul said he had requested meetings with other opposition leaders to seek support for his candidacy.
He did not say whether the MHP would back his bid.
Gul said he would meet with other opposition leaders and hold a press conference to explain his views.
The first round of voting in parliament is scheduled for August 20, the second for August 24, the third for August 28 and the final and fourth round for September.