He becomes the second African-American state schools superintendent in California history.
Outcome of race a major victory for California Teachers Association and allies, and a major defeat for leading charter school advocates.
Thurmond erases 86,000 vote lead by Tuck on Election Day and now has a 75,000 vote lead based on partial count of millions of mail-in and other uncounted ballots.
As of Thursday evening, election results show Marshall Tuck leading Tony Thurmond 50.6 percent to 49.4 percent, a margin of about 69,000 votes.
High-spending campaign for a job with little power but a big megaphone comes down to wire.
View live results from the California Superintendent of Public Instruction race on election night
Contest between Wilson Riles and Max Rafferty in 1970 far more incendiary than current race for state superintendent of public instruction
Whether it's clamping down on charter schools or changing teacher tenure, candidates can say a lot more than they can actually do.
Poll shows Marshall Tuck favored by two-thirds of Republicans, half of independent voters, and one-third of Democrats in the week before the Nov. 6 election.
Marshall Tuck has a more 2-to-1 advantage over Tony Thurmond in direct donations and $28.7 million in funding from independent committees.
Negative ads tie Marshall Tuck to the Trump administration and blame Tony Thurmond for problems in a district where he was a board member.
Committees supporting Marshall Tuck and Tony Thurmond have raised $27.4 million, of which nearly $12 million came in in the last three weeks alone.
With few competitive races on California’s 2018 ballot, the focus of some top donors is shifting to the State Superintendent of Public Instruction race
Tony Thurmond and Marshall Tuck said they support transparency and accountability for charters.
Both say charter schools shouldn't be the focus of the campaign but big independent donors may think otherwise.