He told the marines: “That in no way represents the spirit and the history of the Royal Marines, an outfit that has one of the proudest histories of any in the world.
“We should not let that single incident besmirch the incredible work the Royal Marines have done, not only over decades but over centuries.”
It was the first time in 12 years that a British Marine had been convicted of a war crime.
Two others, known only as Marines B and C, were cleared of murder.
Speaking as the country marks the sacrifice of its war dead on Remembrance Sunday tomorrow, Mr Cameron said it was important to remember those who had lost their lives in more recent conflicts – as well as those from the First and Second World Wars.
Mr Cameron told them: “This is one of the most important weekends of the year when we remember those who have fallen in the service of this country, and it is important we do that with respect.”
Speaking of the government promise to commit £10m to military charities each year, with funding from the fines levied on banks for manipulating Libor rates, Mr Cameron said this was an example of those with the “best values” in society being paid from those who demonstrated the “worst values”.