Flat bands (FBs) and Dirac cones represent two distinctive features of topological electronic systems; however, a unified mechanism enabling transitions between them has remained elusive to date. Here, we demonstrate a symmetry-governed and tunable transition from flat bands to Dirac cones in AB-stacked bilayer kagome lattices. This transition is mediated by the interplay among destructive quantum interference (DQI), $C_3$ rotational symmetry, and spatial inversion symmetry. Strong interlayer coupling enhances DQI and stabilizes compact localized states that produce FBs, while weaker coupling allows $C_3$ and inversion symmetries to dominate, giving rise to robust Dirac nodal points. Using a minimal tight-binding model, we map the continuous evolution of topological states, including type-II and type-III Dirac cones, spin-1 Dirac cones, and partial flat bands, as a function of interlayer coupling. We further demonstrate this transition mechanism by examining an AB-stacked bilayer derived from the experimentally synthesized ${\mathrm{Nb}}_3{\mathrm{TeCl}}_7$ structure. In particular, first-principles calculations on bilayer ${\mathrm{Nb}}_3{\mathrm{TeCl}}_7$ reveal that vertical strain (or pressure) modulates the interlayer interactions, enabling the full FB-Dirac cone transition sequence.These findings establish a realistic pathway for gaining deeper insight into flat-band physics and for engineering tunable topological phases in two-dimensional materials.

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• Dirac fermions
• Electronic structure
• Kagome lattice
• Nodal-line semimetals
• Density functional calculations
• Tight-binding model