The technology executive bought around $1 million (£800,000) in shares on Monday, followed by another $6 million ($4.8 million) on Tuesday, according to an SEC filing.
The purchase is an apparent declaration of confidence in the social network, and Dorsey publicised his purchase by tweeting a link to the SEC filing along with the message: "LoveTwitter".
On Thursday, Twitter announced its fourth-quarter earnings for 2016. It missed analysts' expectations for revenue, and its advertising revenue bookings shrunk 1% year-on-year -; sending its stock tumbling 10%.
Amid an exodus of executives, there are questions about the struggling social network's longterm viability. Dorsey's shopping spree for Dorsey is an apparent signal to investors that he remains deeply committed to the company's fortunes.
According to Recode, the $7 million works out as about 3% of Dorsey's total Twitter stock.