The reception of attitudinal incongruent political information can lead to a reduced willingness for political participation (i.e., behaviors aiming to influence politics). We adopted a metacognitive approach to explain this effect and expected attitudinal (in)congruence to affect the participants’ perceived ease of processing (processing fluency) and self-perception of their issue knowledge (subjective knowledge). Subjective knowledge was repeatedly shown to relate to behavioral outcomes, including political participation, and therefore could explain the attitudinal congruence – participation link. Processing fluency might account for the effect of congruence on subjective knowledge. In our pre-registered online experiment, participants (N = 1.285) saw a political social media post on a political topic (speed limit on German highways vs. extension of the service life of German nuclear power plants). These comments either matched (congruent condition) or contradicted (incongruent condition) the participants’ personal opinions. In accordance with our hypotheses, we found processing fluency, subjective knowledge, and behavioral intentions to be higher in the congruent vs. the incongruent condition (all p-values < .001, d_{ProcessingFluency} = 0.21, d_{SubjectiveKnowledge} = 0.22, d_{PoliticalParticipation} = 0.23). Further, and supporting our remaining hypotheses, we found a positive relationship between processing fluency and subjective knowledge (???? = 0.11, p < .001) as well as between subjective knowledge and behavioral intentions (???? = 0.43, p < .001). Altogether, these findings highlight the importance of considering metacognitive constructs like subjective knowledge to explain political behaviors and suggest that attitudinal congruence might influence the way we perceive our own knowledge and information processing.