The party received 250,388 first preferences, compared with the 184,002 returned for the DUP.
The DUP first preference vote has dropped by about 40,000.
The Alliance Party has increased its first preference vote by about 44,000 to 116,681.
The SDLP polled 78,237 first preference votes – down almost three cent on the 2017 Assembly election.
The DUP and Sinn Féin are vying for top spot in the election, which comes with the entitlement to nominate the next first minister.
While the office of the first and deputy first minister is an equal one with joint power, the allocation of the titles is regarded as symbolically important.
But it is unlikely a new cross-party Executive will be formed as the DUP are refusing to back into the Assembly until the NI Protocol is removed.
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