The government of the semi-autonomous southern Chinese gambling enclave is largely pro-establishment but Sulu Sou, 26, was voted into the legislature in public elections in September.
His party, the New Macau Association, advocates universal suffrage for the territory's parliament, where more than half the representatives are selected by special interest groups or by the pro-Beijing city leader.
The opposition won five of 14 directly elected seats in the 33-strong legislature in September.
A statement from Macau's parliament said 28 lawmakers had voted to suspend him, with four voting against.
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Local media said it meant he could now be investigated on a charge of "aggravated disobedience" over a protest last year. Serving lawmakers are immune from prosecution.
Sou said the move was politically motivated when he addressed a rally before the vote.
"Promise me: don't give up, keep moving forward!" he posted on Facebook after his suspension.
The pro-democracy movement in Macau is far smaller than in nearby Hong Kong, where massive rallies brought several major roads to a standstill in 2014.
Sou was among the leaders of one of Macau's largest anti- government protests in 2014, when 20,000 people demonstrated against generous retirement packages for outgoing officials.
Two pro-independence and four pro-democracy lawmakers have been disqualified from Hong Kong's parliament following a special ruling from Beijing last year.
They were ejected for inserting protests into their oaths of office and accused authorities of a political witch-hunt.
Sou's election victory in September was seen as a slap in the face to local officials over Typhoon Hato, which devastated Macau less than two weeks before the vote.
Some said the government had hesitated to issue a severe storm alert for fear of affecting the casino business.