We create exciton-polaritons in a zero-dimensional (0D) microcavity filled with organic ladder-type conjugated polymer in the strong light-matter interaction regime. Photonic confinement at wavelength scale is realized in the longitudinal direction by two dielectric Bragg mirrors and laterally by a submicron Gaussian-shaped defect. The cavity is separated into two parts, allowing nanometer position control and enabling tuning of the exciton and photon fractions of the polariton wave function. Polariton condensation is achieved with nonresonant picosecond optical excitation under ambient conditions and evidenced by a threshold behavior with a nonlinear increase in the emission intensity, line narrowing, and a blue shift in the emission peak. Furthermore, angular emission spectra show that condensation occurs in the ground state of the 0D cavity, and first-order coherence measurements reveal the coherent nature. These experiments open the door for polariton quantum fluids in complex external potentials at room temperature.