Dendritic cells (DCs) are immune sentinels comprising antigen-presenting conventional DCs (cDCs) and cytokine-producing plasmacytoid DCs (pDCs). The cytokine Flt3 ligand (Flt3L) supports the proliferation of hematopoietic progenitors and is both necessary and sufficient for DC differentiation. To dissect the transcriptional control of Flt3L-driven DC differentiation, we previously performed an unbiased genome-wide CRISPR/Cas9-based dropout screen using the Flt3L-dependent murine cell line HoxB8-FL. Our screen identified the transcriptional repressor Trim33 (TIF1-γ) as an essential regulator of DC differentiation. In vivo conditional targeting confirmed the absolute, cell-intrinsic requirement for Trim33 in the emergence of DC progenitors and mature DCs, as well as in the maintenance of mature cDC1s. We now undertook a kinetic analysis of Trim33 deletion and found that it causes the collapse of pDCs and cDC1s in peripheral tissues, as well as of their BM progenitors, as early as two days post-deletion. We also performed single-cell transcriptomic profiling of Flt3+ BM progenitors shortly after Trim33 deletion. We found that it causes de-repression of Trim33 target genes in myeloid progenitors, as well as the rapid loss of all identifiable pDC and cDC1 progenitors. In contrast, lymphoid progenitors were unaffected by Trim33 deletion. Finally, DC-specific targeting of Trim33 confirmed its essential role in the maintenance and maturation of cDC1. Taken together, our results identify Trim33 as an essential regulator of the entire DC lineage, demonstrating a critical dependence of the pDC and cDC1 lineages on Trim33 for their differentiation and early homeostatic maintenance.