Mr Rajab was sentenced in 2018 to five years in prison for tweeting about Saudi Arabia’s involvement in the war in Yemen.
He has been an outspoken critic of the Bahraini government and played a prominent role in pro-democracy protests in February 2011.
Rajab was released after a court agreed to pass an alternative to the jail term he received, his lawyer added.
A former President of the Bahrain Centre for Human Rights, Rajab played a central role in the pro-democracy protests that swept the country during the wider Arab Spring movement.
He continued to criticise the Bahrain government after it announced a state of emergency in response to the uprising and later became known as “unofficial leader of the 14 February movement” .