Elon Musk has quietly funneled more than $276 million into Republican groups and his super PAC since the start of July, building a huge turnout operation to help the party battle headwinds in the midterm elections.

The staggering amount of money makes Mr. Musk, the richest person in the world, by far the largest known donor in the midterms. Representatives for Mr. Musk supplied the previously unreported figures on his political giving to The New York Times before a federal filing deadline on Thursday.

In an effort to save Republicans’ Senate majority, he gave a total of $158 million this summer to the Senate Leadership Fund, the main super PAC backing the party’s candidates for the chamber, according to his team. In sum, that is one of the largest political donations in American history, and more than the group’s Democratic rival raised from all of its donors that quarter.