Abstract We document an increase in market power for politically active firms during times of heightened policy uncertainty, when their information and influence advantage is greater. The effect is long-lasting and stronger for large politically active firms. We show that relatively large investments during high uncertainty periods serve as a potential mechanism for gains in market power. Industries populated with politically active firms experience lower business dynamism and import penetration, consistent with active firms leveraging investment timing to restrict competition. Results suggest that political activism is a likely contributing factor to the dominance of large firms over the last two decades.