This dissertation presents the measurement of the t-channel production of single top quarks and antiquarks using the complete Run 2 dataset recorded by the ATLAS detector. The cross-section of the process is measured separately for top quark and top antiquark production. Additionally, the ratio of these cross-sections, denoted as R_t, is also determined. The methodology involves a cut-based selection, a neural network for signal separation, and a binned maximum likelihood fit. The full Run 2 dataset from the ATLAS detector encompasses an integrated luminosity of 140 fb -1 from proton-proton collisions at a center-of-mass energy of 13 TeV. The total cross-sections are measured to be 137 +8 -8 pb for top-quark production and 84 +6 -5 pb for top-antiquark production. The combined cross-section is determined to be 221 +13 -13 pb, and the cross-section ratio is R_t = 1.636 +0.036 -0.034. The measured cross-sections align well with the predictions made at the next-to-next-to-leading order in quantum chromodynamics. The measured total cross-section is further used to derive a constraint on the CKM matrix element |V_