Nowadays, the global brick industry utilizes billions of cubic meters of clay soil annually, resulting in the massive consumption of non-renewable resources. This study explores the viability of utilizing red marl from phosphate mining waste rocks for fired brick production. Ecofriendly fired bricks produced from 100% side streams (red marly clays (RM) and marble waste powder (MWP)) were prepared, pressed, dried at 105 °C, and then fired at 1100 °C for 1 h. The effects of marble waste powder addition (up to 30 wt%) on the physical, mechanical, mineralogical, and microstructural properties of the fired bricks were explored. The main results show that fired bricks with high compressive strength of a maximum of 39 MPa could be prepared with a mixture of red marl and 10 wt% of marble waste powder. The thermal conductivity was decreased by marble waste addition (from 0 to 30%) and was reduced from 0.93 W/m.k to 0.53 W/m.k; however, the compressive strength was also decreased to reach a minimum of 17 MPa. The firing shrinkage and density were also reduced with 30% marble waste by 41% and 18%, respectively. Therefore, red marly clays and marble waste could be promising raw materials for eco-fired brick production.