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This paper analyzes the effect of both solidification and heat treatment process on microstructure, microhardness, electrical resistivity and electrical conductivity (ρ and σ) in an Al–3Cu–5Nb alloy (mass/%). In this sense, an unsteady-state horizontal solidification experiment was carried out using a water-cooled solidification device and as-cast samples were subjected to various T6-type heat treatment conditions. The solidification thermal parameters investigated were the growth and cooling rates (VL and TR), and those of the thermal treatment were the temperatures and times in the solution and aging stages. Techniques by optical and scanning electron microscopy differential scanning calorimetry (DSC) and X-ray diffractometry (XRD) were applied for microstructural and thermal analysis. The DSC results showed the plateau corresponding to the beginning and end of the formation of the Al-rich solid solution (Alα), indicated by the TLα and TS/eutectic temperatures of the alloy (~ 645 °C and ~ 530 °C). An increase in the HV values with the application of the T6-heat treatment in the as-cast samples was observed for all assumed conditions and the best condition found was for 500 °C/3 h of solution, and 155 °C/5 h for the aging in which the hardness increased from 61.4 to 90.33 HV, equivalent to the increase of ~ 47%. It was observed that macrostructure consisting of columnar grains favor electric current flow contributing to the decrease of ρ, as a consequence increased σ. For the total length of the ingot, the electrical conductivity increased from 23.8 × 106 S m−1 in the solidified conditions to 40.1 × 106 S m−1 (~ 68.5%) in the T6 conditions equal to 490 °C/3 h and 155 °C/3 h in the solution and aging stages, respectively, as well as higher σ values were found in the region formed by columnar grains in which higher VL and TR values and lower secondary dendritic spacing (λ2) were obtained. [ABSTRACT FROM AUTHOR]