At the investigative journalism site, The Markup, Mattu created Blacklight, a real-time website privacy inspector, and led Citizen Browser, a first of its kind independent audit of Facebook’s recommendation algorithms. Mattu’s work at The Markup has received public recognition, including two Edward R. Murrow awards and an award from the National Association of Black Journalists. He is also a 2021 University of Michigan Knight Wallace fellow.

Previously, he was a contributing researcher at ProPublica, where he worked on Machine Bias, a series that aims to highlight how algorithmic systems can be biased and discriminate against people. Machine Bias was a Pulitzer Prize finalist for Explanatory Journalism. His work has been exhibited at Somerset House, The Haus der Kulturen der Welt , The Whitney Museum, V&A Museum and Bitforms Gallery.