The digital distributor has almost doubled its total in nine months, reports The Beat.
"This has been a banner year for comiXology," said co-founder and CEO David Steinberger in a statement. "We have dedicated ourselves to expanding the comic book audience by delivering the best consumer experience, and it's fantastic to see that unfold.
"We started the year cresting 50 million downloads, two and a half years after launch; we added the next 50 million more than three times as fast. We are spreading the love of comics."
The company will celebrate the run-up to its milestone by offering a different comic to download for free each day.
"It's dizzying to look back at the last twelve months and see that we've been the top-grossing iPad app in the entire iTunes App Store almost 90% of all Wednesdays," added co-founder John D Roberts.
"ComiXology's mission is to bring comics to everyone everywhere and - looking at crossing this 100 million download milestone - it certainly feels like we are making good on that promise."