The entrepreneur Andrew Yang announced Wednesday that his presidential campaign had raised $10 million in the third quarter of 2019, a significant sum for the political outsider who was almost entirely unknown when he began his long-shot bid for the Democratic nomination 20 months ago .

The $10 million raised from July to September is more than three times what Mr. Yang’s campaign raised during the previous quarter and almost double what the campaign brought in through June 30. The total is expected to land him in the top third of the 19-candidate field and signals that there is financial backing behind Mr. Yang’s steady if modest support in the polls.

Aides said Mr. Yang had received about 300,000 contributions from unique donors over the course of his campaign, but did not disclose how many individuals gave in the third quarter specifically. The average donation during the past three months was around $30, and 99 percent of the donations were $200 or less, Mr. Yang’s campaign said. Overall, it had $6.3 million cash on hand.

The sale of campaign merchandise — including at least 20,000 “MATH” hats — accounted for about $2.4 million of the money raised in the third quarter, aides said.