It will use Thunderclap to allow Twitter and Facebook users to simultaneously send the same message.
The message: "I'll be remembering the fallen at 11 o'clock #2MinuteSilence #LestWeForget," will be sent at 09:00 GMT on Remembrance Sunday.
Thunderclap has been used by the UN to support World Humanitarian Day.
The charity hopes thousands of the UK's estimated 10 million Twitter and 33 million Facebook users will take part in The Royal British Legion's Two Minute Silence Thunderclap.
Helen Hill, head of remembrance at The Royal British Legion, said: "We hope to create the largest ever show of online remembrance by using the communicative power of social media to remind millions of Britons that they have a very personal opportunity to honour the men and women who paid the ultimate sacrifice."
Thunderclap describes itself as the "first-ever crowdspeaking platform that helps users be heard by saying something together" and has been used by a number of international charities and causes.
Hashem Bajwa, spokesman for Thunderclap, said: "Twitter is a wonderful way to say something, but it's difficult to be heard.
"Thunderclap lets people be heard by saying something together."
The act of observing a two-minute silence began in 1919 following the Armistice at 11am on 11 November 1918 at the end of World War I.
The Royal British Legion is the UK's leading armed forces charity and it ensures those who gave their lives in wars and conflicts are remembered.
The Royal British Legion says it is to be the first UK organisation to use a social media tool to encourage people to mark the two-minute silence.