Spiegel converted and sold about 1.5 million shares at $16.66 to $17.63 per share, the documents say. The shares will be used to cover Spiegel's taxes on his three-year restricted stock unit award program, which began a year ago.
That plan was detailed in Snap's first annual report as a public company, released late last month. Spiegel's post-IPO bonus was worth $637 million and represented 3 percent of the total shares outstanding at the time of the IPO.
Snap went public last year, and initial public offerings are a common way that start-up founders and investors can liquidate paper gains in their companies.
Spiegel has held off until recently, after telling investors last year that he would not sell any shares for the remainder of the 2017 calendar year after the IPO. Spiegel's first major share sale of $50 million was reported last month.
Snap shares were down a little more than 1 percent Monday morning after a week of volatile trading. But at nearly $18 a share, the stock was still holding above last year's IPO price, after first dipping below $17 in July.
Disclosure: CNBC parent NBCUniversal is an investor in Snap.