Twenty-year-old Redha Mohammed died at a clinic after being shot by the military during a protest on Friday, said Abdel Jalil Khalil Ibrahim, the head of the Shiite INAA opposition parliamentary group.
His death brings to seven the number of demonstrators killed since anti-regime protests began on February 14, according to an AFP tally based on relatives of victims and opposition officials.
Pearl Square has been the focal point of anti-regime demonstrations in the Gulf kingdom of Bahrain, which has a Shiite majority but is ruled by a Sunni dynasty.
An early morning raid on Thursday resulted in the deaths of four people and was followed by the army deploying in the square, but protesters flocked back on Saturday after the army was ordered back to base.
Riot police fired tear gas in an unsuccessful attempt to disperse them but then withdrew as Crown Prince Salman, deputy commander of the armed forces, ordered both police and troops to hold back.
After their first night since returning to the square passed peacefully, protesters erected more tents on Sunday afternoon, signalling they were not planning to leave any time soon.