About 80% of democracies allow legislators to be employed in the private sector while they hold office. However, we know little about the consequences of this practice. In this article, I use newly assembled panel data of all members of the United Kingdom House of Commons and a difference-in-differences design to investigate how legislators change their parliamentary behavior when they have outside earnings.

When holding a private sector job, members of the governing Conservative Party, who earn the vast majority of outside income, change whether and how they vote on the floor of parliament as well as increase the number of written parliamentary questions they ask by 60%. For the latter, I demonstrate a targeted pattern suggesting that the increase relates to their employment.

The article thus shows that one of the most common, and yet least studied, forms of money in politics affects politicians’ parliamentary behavior.