The metastatic progression of cancer is a multi‐step process initiated by the local invasion of the peritumoral stroma. To identify the mechanisms underlying colorectal carcinoma (CRC) invasion, we collected live human primary cancer specimens at the time of surgery and monitored them ex vivo. This revealed that conventional adenocarcinomas undergo collective invasion while retaining their epithelial glandular architecture with an inward apical pole delineating a luminal cavity. To identify the underlying mechanisms, we used microscopy‐based assays on 3D organotypic cultures of Caco‐2 cysts as a model system. We performed two siRNA screens targeting Rho‐GTPases effectors and guanine nucleotide exchange factors. These screens revealed that ROCK2 inhibition triggers the initial leader/follower polarization of the CRC cell cohorts and induces collective invasion. We further identified FARP2 as the Rac1 GEF necessary for CRC collective invasion. However, FARP2 activation is not sufficient to trigger leader cell formation and the concomitant inhibition of Myosin‐II is required to induce invasion downstream of ROCK2 inhibition. Our results contrast with ROCK pro‐invasive function in other cancers, stressing that the molecular mechanism of metastatic spread likely depends on tumour types and invasion mode. Synopsis Metastatic progression is initiated by local invasion of the peritumoral stroma, but the mechanisms underlying cancer cell migration remain unclear. Here, histological analyses of human primary colorectal carcinomas (CRC) combined with screenings of live ex vivo 3D cultures determine the mode of dissemination and identify the Rho‐GTPase signalling effectors involved. Conventional CRC cells invade collectively as differentiated epithelial glands with retained apico‐basolateral polarity. ROCK2 kinase inhibition triggers leader‐cell formation and dissemination of patient‐derived xenograft explants. ROCK2 blocks guanine exchange factor FARP2 recruitment to the apical junctional complex. FARP2 activation and Myosin‐II inhibition cooperate in collective invasion. Colorectal cancer specimens show coordinated gland‐like dissemination controlled by Rho‐GTPase signalling.