Clinically impairing irritability and temper outbursts are among the most common psychiatric problems in youth and present transdiagnostically; however, few mechanistically informed treatments have been developed. Here, we test the acceptability, feasibility, and preliminary efficacy of a novel exposure-based treatment with integrated parent management skills for youth with severe irritability using a randomized between-subjects multiple baseline design. N = 41 patients (Age, Mean (SD) = 11.23 years (1.85), 62.5% male, 77.5% white) characterized by severe and impairing temper outbursts and irritability were randomized to different baseline observation durations (2, 4, or 6 weeks) prior to active treatment; 40 participants completed the 12 session treatment of exposure-based cognitive-behavioral therapy for irritability with integrated parent management skills. Masked clinician ratings were acquired throughout baseline and treatment phases, as well as 3- and 6-months post-treatment. To examine acceptability and feasibility, drop-out rates and adverse events were examined. Primary clinical outcome measures included clinician-administered measures of irritability severity and improvement. Secondary clinical outcome measures included multi-informant measures of irritability, depression, anxiety, and attention-deficit/hyperactivity disorder symptoms. No patients dropped out once treatment began, and no adverse events were reported. Irritability symptoms improved during the active phase of treatment across all measurements (all βs > -0.04, ps < .011, Cohen's d range: -0.33 to -0.98). Treatment gains were maintained at follow-up (all βs (39)  < -0.001, ps > .400). Sixty-five percent of patients were considered significantly improved or recovered post-treatment based on the primary clinician-rated outcome measure. Results support acceptability, feasibility, and preliminary efficacy of this novel treatment for youth with severe irritability. Limitations and future directions are also discussed.