Significance of superplasticizers (SPs) in sustainable development of concrete industry is well known regarding to reduced water and Portland cement content of the mixtures. Development of eco-efficient alternative types of SPs is needed. A humic-acid based superplasticizer derived from leonardite (LHA) as a natural organic matter was examined in terms of its plasticizing performance and influence on hydration as well as properties of Portland cement (PC) in comparison with lignosulfonate- (LS) and naphthalene-based admixture (NA). The impact of LHA on hydration of Portland cement was investigated for various dosages of addition by isothermal calorimetry and thermo-gravimetric analysis of hardened pastes. In addition, effect of admixtures on setting time of PC pastes as well as flow and compressive strength of mortars were also studied. Experimental results indicated that LHA has similar impact on early hydration kinetics and setting time of PC when compared to NA. However, LS caused dramatic retardation on PC hydration. LHA addition was also increased the degree of hydration of PC both at 7 and 28 days, and this increasing was more pronounced at 7 days. LHA showed a comparable plasticizing performance to the other admixtures as measured by flow of mortars for 0.3% equivalent solid dosage. Compressive strength of mortars with LHA addition was higher than that of control PC mortar at 3, 7 and 28 days of age for all the dosages tested. LHA was found to have a considerable potential for use as superplasticizer in cementitious systems with its reasonable effects on hydration and properties of PC.