Rwanda has become the 54th member of the Commonwealth.
The African country was admitted at the Commonwealth Heads of Government meeting in Trinidad and Tobago at the weekend.
Rwanda has been rebuilding its economy after a 1994 ethnic genocide that killed 800,000 people.
Pressure groups had urged Commonwealth leaders not to accept the country, due to its record on human rights and corruption, the BBC reports.
A Rwandan minister said the move showed his country's "tremendous progress" over the past 15 years.
Rwanda, a former colony of Germany and Belgium, is the second country to be admitted without a British colonial past or constitutional link to Britain.
Mozambique is the only other Commonwealth member without historic UK ties. It joined the organisation 14 years ago.