The couple were snapped walking in London indulging in a series of kisses showing their delight at being engaged.
She showed off her engagement ring, which consists of a single diamond set into a thin gold band. The actress was also seen wearing a silver love ring on her left hand.
Last week, a publicist confirmed the news that the pair were engaged to be married after 15 months of dating.
They are known for being private and have never attended a public event together but they are often seen walking arm in arm around London.
Knightley met Righton, who is the keyboardist in the indie band The Klaxons, through their mutual friend Alexa Chung.
It is not known how Righton proposed to the Pirates of the Caribbean actress and no details about the wedding have yet emerged.