William Hague has hailed an historic moment for Egypt tonight after Mohammed Morsi was elected president.
The Foreign Secretary congratulated the Muslim Brotherhood candidate on securing 51% of the vote in a run-off between the Islamist party and former Prime Minister Ahmed Shafiq.
He urged the new premier to focus on national unity, reconciliation and human rights in the wake of the Arab Spring revolution that saw Hosni Mubarak deposed.
Mr Hague said in a statement: "I congratulate the Egyptian people for their commitment to the democratic process and electing a new President of Egypt. I wish Dr Mohammed Morsi success in the challenging task ahead.
"This is an historic moment for Egypt. I welcome President Morsi's statement that he intends to form an inclusive government that governs on behalf of all the Egyptian people.
"It will be important for the new government to stand for national unity and reconciliation, to build bridges across Egyptian society and to uphold human rights, including the rights of women and religious minorities, and the rule of law.
"An inclusive government with the authority to take forward reforms, and a new Parliament and Constitution which represent the interests of all Egyptians, will be important steps in Egypt's transition to democratic government.
"Britain will support the Egyptian people and their leaders as they take steps to consolidate their democratic rights and institutions and to reinvigorate the Egyptian economy.
"We value our long-standing partnership with Egypt, including on regional issues, and look forward to working with President Morsi and his government to support the process of democratic transition and to promote our common interest in security, stability and prosperity."
The news that Mr Morsi had defeated ex-prime minister Ahmed Shafiq, despite the election regulator upholding some complaints, prompted scenes of jubilation in Cairo's Tahrir Square.
The new president's supporters have maintained a vigil there for days in protest at decrees by the ruling Supreme Council of the Armed Forces (Scaf) seemingly designed to reduce or constrain the power of the president.
There have also been complaints that turnout was low because voters only had a choice between the Muslim Brotherhood and a former member of Mubarak's regime in the run-off.
Shadow foreign secretary Douglas Alexander added his congratulations after the long-awaited result was declared.
"All parties must now commit to working together to establish democratic institutions, agree a constitution which respects individual rights, and build good relations with neighbours in the interests of the region and the wider world," he added.