Flt3L/Flt3 pathway governs conventional dendritic cell (cDC) development and function; however, clinical trials with Flt3L have shown limited efficacy, underscoring the need to better understand Flt3 regulation to improve therapeutic strategies. To identify regulators of Flt3, and thereby regulators of cDC development, a CRISPR/Cas9 genome wide knock out screen was performed. This screen identified ubiquitin-specific peptidase 22 (USP22) as a positive regulator of Flt3 expression by Mutu DCs. Usp22 deletion in vitro and in vivo resulted in reduced development of cDC1. This was evidenced as a reduction in the number of cDC1 and a marked decrease in cDC1 markers including CD8α, XCR1, and DEC205. The impact of USP22 on cDC1 development is largely due to a developmental block at the pre-DC progenitor stage in the bone marrow. RNA sequencing (RNA-seq) of MuTu DCs that lacked Usp22, overexpressed wild type Usp22 or overexpressed C185S catalytic mutant Usp22 showed that loss of Usp22, or its catalytic activity, resulted in reduced expression of Flt3, Irf8, Cd8a and Cd24a, genes known to be associated with cDC1s. Increased H2Bub1, but not H3K9ac, was also observed in these cells, suggesting USP22 likely impacts cDC development through epigenetic mechanisms. Finally, in vitro treatment with USP22i-S02, a USP22 inhibitor, significantly reduced cDC1s, suggesting that USP22 is a promising target for modulating dendritic cells in immunotherapy. In summary, our study identifies USP22 as a pivotal regulator of cDC1 development and highlights its potential as a therapeutic target to modulate cDC1 mediated immunity.