A macro rectangular-channel flat-plate solar thermal collector is designed and examined in this study. It consists of a set of adjacent macro rectangular channels formed between the upper, lower, and fin-parts of an absorber plate, thus, overcoming the necessary welding between the absorber plate and riser tubes used in conventional flat-plate collectors. An optimization model is suggested and solved to obtain an optimal design of the proposed collector. After that, a detailed dynamic mathematical model of this collector is presented and numerical simulation is carried out using matlab. Furthermore, a comparison with a conventional sheet-and-tube solar thermal collector is investigated and parametric analysis is conducted under both steady-state and dynamic conditions. The results reveal that the designed collector yields an enhancement of 8% for integrated thermal efficiency under transient regime and an average improvement of 12% for steady-state efficiency when compared with the conventional collector. In addition, the influence of the variation of different parameters, such as the mass flow rate of the heat transfer fluid (HTF), the thickness of different parts of the absorber plate, and the number of channels, on the performance of the proposed collector is presented. From an economical perspective, the cost of materials composing the new collector is less than that of materials composing the conventional one.