The purpose of the study is to evaluate whether encorafenib plus cetuximab (EC), alone or in combination with chemotherapy, can improve clinical outcomes relative to current standard of-care chemotherapy in participants with previously untreated BRAF V600E-mutant mCRC. Since encorafenib has not previously been combined with chemotherapy, the tolerability and PK of EC in combination with mFOLFOX6 and in combination with FOLFIRI will be evaluated in separate cohorts in the safety lead-in portion of the trial in order to identify which chemotherapy combination is to be used in the Phase 3 portion of the study.