In this paper, a broadband absorber utilizing monolayer molybdenum disulfide (MoS2) is proposed, and a generalized interference theory (GIT) is derived to investigate this absorber. Using the hybrid Lorentz-Drude and Gaussian model of monolayer MoS2 and the dyadic Green's functions, the propagation properties of monolayer MoS2 are first investigated. Then, a sandwich-like MoS2-based absorber design is proposed in the visible regime. The sandwich-like structure is mounted on a fully reflective gold mirror, which forms a Fabry-Perot resonator to strengthen light-matter interactions and enhance the absorption. To numerically calculate the absorption performance of this absorber, the GIT is next derived from interference theory. The numerical results indicate that an absorption ≥ 90% is obtained for a range of wavelengths (λ) from 389 to 517 nm, and this absorber can operate well, even with an angle of incidence up to 60°, which also verifies the prediction of the MoS2-based absorber mainly operating at λ < 700 nm. Afterward, the operating mechanism of the proposed design is determined using the theory of destructive interference. Finally, the proposed design and derived GIT are validated by a simulation using commercial electromagnetic software. The derived GIT drives the numerical investigation of the multilayer structure with various polarization types and angles of incidence of the waves, and the MoS2-based absorber can be used in several applications such as photoelectric storage and photoelectric detection.