Understanding the excited-state charge carrier relaxation in metal-organic frameworks (MOFs) and revealing ways to alternate its rate are of primary importance for the development of novel hybrid photoactive materials with sufficiently long carrier lifetimes; in particular, shedding light on the main recombination pathways in this class of compounds is needed. Therefore, in this work the radiative and phonon-assisted nonradiative electron-hole recombination is investigated theoretically for a model MOF system, and the nonradiative pathway is demonstrated to be dominant even for a pristine defect-free material. Theoretically predicted electron-hole lifetimes are in line with the available experimental data, suggesting that the adopted methodology is suitable for prediction of carrier lifetimes and helpful for the interpretation of experimental data. Based on the obtained conclusions, the principles for modification of MOF geometrical and chemical structure, enabling the extension of carrier lifetimes, are formulated.