Senator Elizabeth Warren, who entered the presidential race loudly denouncing the influence of super PACs and big money in politics, will now be the beneficiary of what is believed to be the largest ad buy by a super PAC in the 2020 Democratic primary.

The super PAC, known as Persist PAC, announced late on Thursday night that it was buying $9 million in television and digital ads across nine expensive media markets in three Super Tuesday states: California, Texas and Massachusetts. The reservation is in addition to another $3.25 million previously announced that covers seven other states, plus California.

Because the super PAC was formed so late — it launched days before the Nevada caucuses — the group can keep its donors secret from the millions of Americans who will be voting in the coming weeks. A representative for the group said it would not disclose its donors until legally required, on March 20. At that point, about 60 percent of the delegates in the country would be allocated.

Ms. Warren’s campaign did not respond to a request for comment about whether the names of donors should be released sooner.