Britain's Queen Elizabeth II was on Monday to sign a charter calling for an end to discrimination across the 54 Commonwealth nations, Buckingham Palace said.
The monarch, who was recently hospitalised after contracting gastroenteritis, will authorise the document at a London event celebrating Commonwealth Day.
"We are implacably opposed to all forms of discrimination, whether rooted in gender, race, colour, creed, political belief or other grounds," the document reads.
All of the Commonwealth nations adopted the charter in December.
The 16-point charter aims to protect democracy, the rule of law, international security and free speech.
A Buckingham Palace spokesman said: "At a Commonwealth event on Monday, the Queen will sign a charter agreed upon by the 54 members of the Commonwealth.
"The Queen, as in all matters, is apolitical but is signing the document in her capacity as head of the Commonwealth."
Gay rights campaigner Peter Tatchell praised the accord, despite there being no explicit provisions against the discrimination of homosexuals.
"By signing the new Commonwealth Charter, with its rejection of all discrimination, the Queen is implicitly endorsing gay human rights," he said.
"Although the charter does not include an explicit commitment to gay equality, the clause rejecting discrimination based on 'other grounds' implicitly includes a rejection of homophobic discrimination.
"To secure that insertion was a long, tough battle," he added.
The veteran campaigner blamed "the homophobic majority of member states" for blocking explicit attempts to protect homosexuals.