<p>Eukaryotic cells license far more potential replication origins than they use, but how origin firing rate is tuned in S phase,&#xa0;especially under replication stress, remains unclear. Here, we identify a regulatory mechanism by which cyclin-dependent kinase (CDK) activity controls the abundance and chromatin recruitment of the origin firing factors TRESLIN and MTBP to promote dormant origin activation. Inhibition of WEE1 kinase during S phase increases CDK activity, which blocks the PCNA-CRL4^CDT2-dependent degradation of TRESLIN and enhances its chromatin association along with MTBP. This increased loading is required for elevated helicase recruitment and DNA synthesis under CDK-hyperactive conditions. We define a sequence within TRESLIN required for its degradation and show that TRESLIN stabilization is necessary but not sufficient for CDK-driven origin firing. Replication stress regulates TRESLIN destruction in a dose- and time-dependent manner. Acute high-dose hydroxyurea suppresses CDK activity and reduces chromatin-bound TRESLIN, whereas prolonged low-dose hydroxyurea is accompanied by elevated CDK activity and increased chromatin loading of TRESLIN–MTBP and CDC45. Altogether, these findings uncover a control point in replication origin usage with implications for genome stability and therapeutic kinase inhibition.</p>