Quantum phase transitions (QPTs) describe when a many-body quantum system displays non-analytic behavior associated with a discontinuous change in a property of the ground state as a parameter is varied. The QPT in prototypical Dicke model is difficult to reach experimentally as the spinfield coupling strength must be quite large. In this work we describe a new modelthe off-resonant TavisCummings model where we drive the common mode, and discover a new type of QPT at quite low coupling strengths which are comparable with the geometric mean of the atomic and field detunings λ∼ λc≡√ΔaΔc. Through analytic methods we demonstrate this QPT for both finite and infinite numbers of spins and show that |〈Jx (Jz)〉|/(N/2) ∼|λ/ λc - 1|λx(λ(Z) (z ) and 〈aa〉/N ∼ |λ/ λc - 1| λa for λ ≥ λc, with critical exponents λx ≈ 1/2, λz ≈ 1 and λa ≈ 1. We show that this QPT can be immediately observed by laboratory cavity-QED setups such as BoseEinstein condensate in optical cavity and superconducting circuit-QED as well as a line of trapped ultracold ions.