This paper aims to investigate the numerical approximation of semilinear non-autonomous stochastic partial differential equations (SPDEs) driven by multiplicative or additive noise. Such equations are more realistic than the autonomous ones when modeling real world phenomena. Such equations find applications in many fields such as transport in porous media, quantum fields theory, electromagnetism and nuclear physics. Numerical approximations of autonomous SPDEs are thoroughly investigated in the literature, while the non-autonomous case is not yet well understood. Here, a non-autonomous SPDE is discretized in space by the finite element method and in time by the linear implicit Euler method. We break the complexity in the analysis of the time depending, not necessarily self-adjoint linear operators with the corresponding semigroup and provide the strong convergence result of the fully discrete scheme toward the mild solution. The results indicate how the converge order depends on the regularity of the initial solution and the noise. Additionally, for additive noise we achieve convergence order in time approximately 1 under less regularity assumptions on the nonlinear drift term than required in the current literature, even in the autonomous case.Numerical simulations motivated from realistic porous media flow are provided to illustrate our theoretical finding.We consider numerical approximation of the following non-autonomous SPDE defined in Λ ⊂on the Hilbert space L 2 (Λ, R), T > 0 is the final time, F and B are nonlinear functions and X 0 is the initial data, which is random. The family of linear operators A(t) are unbounded, not necessarily self-adjoint, and for all s ∈ [0, T ], −A(s) is the generator of an analytic semigroup S s (t) =: e −tA(s) , t ≥ 0. The noise W (t) is a Q−Wiener process defined in a filtered probability space (Ω, F , P, {F t } t≥0 ). The filtration is assumed to fulfill the usual conditions (see e.g. [38,Definition 2.1.11]). Note that the noise can be represented as follows (see e.g. [38,37])where q i , e i , i ∈ N d are respectively the eigenvalues and the eigenfunctions of the covariance operator Q, and β i , i ∈ N, are independent and identically distributed standard Brownian motions. Precise assumptions on F , B, X 0 and A(t) will be given in the next section to ensure the existence of the unique mild solution X of (1). In many situations it is hard to exhibit explicit solutions of SPDEs. Therefore, numerical algorithms are good tools to provide realistic approximations. Strong approximations of autonomous SPDEs with constant linear self-adjoint operator A(t) = A are widely investigated in the literature, see e.g. [47,46,20,17,25,48] and references therein. When we turn our attention to the case of semilinear SPDEs, still with constant operator A(t) = A, but not necessary self-adjoint, the list of references becomes remarkably short, see e.g. [24,31]. Note that modelling real world phenomena with time dependent linear operator is more realistic than modelling with time independent lin...