Johnston is the author of eight books, four of them bestsellers. His 1992 debut, Temples of Chance, examined corruption in the casino industry. Perfectly Legal (2003) and Free Lunch (2007) analysed how tax policies and corporate practices disadvantage ordinary Americans.
Divided (2014) examined income inequality, and his 2016 book The Making of Donald Trump offered a critical look at Trump's rise. In 2018, Johnston published It's Even Worse Than You Think, detailing the impact of the Trump administration's policies.