This paper investigates the robust $H_{\infty }$ observer-based control (OBC) for linear time-invariant disturbed uncertain fractional-order systems (DU-FOS). First, the existence conditions for robust $H_{\infty }$ OBC are given. Then, based on the $H_{\infty }$ -norm analysis using the generalized Kalman–Yakubovich–Popov lemma for FOS, and following the fractional derivative order $\alpha$ , new sufficient linear matrix inequalities (LMIs) conditions are obtained to ensure the stability of the estimation errors and the stabilization of the DU-FOS simultaneously. All observer matrices gains and control laws can be computed by solving a unique LMI condition in one step. Numerical simulation is given to illustrate the validity of the proposed method.