The phrase "affirmed their commitment to" is correct and usable in written English.
You can use it when expressing a strong dedication or promise to a cause, goal, or principle.
Example: "The organization affirmed their commitment to environmental sustainability during the annual conference."
Alternatives: "reiterated their dedication to" or "confirmed their pledge to".
Talking Heads' choice of Brian Eno as producer affirmed their commitment to creative growth.
At least 13 players currently listed as first-stringers affirmed their commitment to staying, including quarterback Matt McGloin.
Ghannouchi and other leaders affirmed their commitment to democratic rights and excluded references to Sharia law in the new constitution.
Members of the international community, however, quickly affirmed their commitment to trading exclusively with the Tripoli-based NOC.
More than 150 of the largest U.S. corporations (even major oil companies) have affirmed their commitment to act on climate.
In another counterpoint to Trump, Merkel and Peña Nieto together affirmed their commitment to free trade during the German leader's visit to Latin America's second-biggest economy.
In major breakthrough, Education Ministers meeting held in 2007, Pacific countries endorsed and affirmed their commitments to develop a national policy for children aged 0-8 years by 2010 paving way for attention to this underserved issue.
Donald Trump and Theresa May have re-affirmed their commitment to the US/UK special relationship during a short but friendly news conference in the White House.
At the GCC summit at the end of 2007 the member states re-affirmed their commitment to the target of achieving monetary union in 2010, while stating that this would only apply to those states which were ready for such a move (Oman has already opted out).
Mexico's congressional leaders have been more positive, affirming their commitment to nearly all these proposals.
They should affirm their commitment to assist the Palestinian Authority and get the funds flowing.
