The biomass production from Leucaena leucocephala (Lam.) de Wit (family Fabaceae) is a valuable source for chemical biorefinery. The bioactive molecules from the methanol extracts (MEs) from various parts of L. leucocephala grown in Egypt were evaluated. The antibacterial activity against the growth of Erwinia amylovora, Agrobacterium tumefaciens, and Staphylococcus aureus was determined by the inhibition zones (IZs) and the minimum inhibitory concentrations (MICs). The antifungal activity against the growth of Rhizoctonia solani, Fusarium solani, and Alternaria solani was recorded by measuring the fungal growth inhibition (FGI %) and MICs. The phytochemical compounds in the MEs were identified by HPLC–DAD, where the higher compounds identified (mg/kg ME) in seeds were benzoic acid (1520.44), myricetin (848.73), and rosmarinic acid (792.46); in roots, were benzoic acid (554.04), naringenin (419.99), and myricetin (205.51); in leaves were rosmarinic acid (4768.16), resveratrol (2983.99), quercetin (2052.43), myricetin (1432.63), and naringenin (1182.39); in branches, were rosmarinic acid (2230.26), resveratrol (1605.3), o-coumaric acid (691.16), and myricetin (681.93); in fruits were rosmarinic acid (431.43) and resveratrol (261.07); in stem-wood, were ellagic acid (1319.75), p-coumaric acid (1051.59), and ferulic acid (512.45); and in stem-bark, were resveratrol (1079.01), benzoic acid (1071.11), and catechol (305.51). The MEs at the concentration of 4000 mg/L from stem-wood, leaves, and stem-bark, the higher IZs against the growth of E. amylovora, A. tumefaciens, and S. aureus with values of 4.06 cm, 2.5 cm, and 2.63 cm, respectively, were found. The range of MICs values of MEs was 75–500 mg/L, 75–125 mg/L, and 75–125 mg/L, against the growth of A. tumefaciens, E. amylovora, and S. aureus, respectively. MEs prepared from seeds, fruits (pod), and stem-bark at 4000 mg/L showed the higher FGI (100%) against the growth of A. solani; MEs from seeds and branches observed the higher FGI values of 63.83% and 63.6%, respectively, against the growth of F. solani, and all MEs showed potent antifungal activity (FGI 100%) against R. solani except for leaf ME (88.06%). MICs were in the range of 250–500, 250–500, and 500–1000 mg/L against A. solani, F. solani, and R. solani, respectively. At 500 mg/L, the roots ME showed the highest total antioxidant activity (94.30%) compared to vitamin C (VC) (98.30%) at 100 mg/L. The EC50 values of the MEs from seeds, fruits, stem-bark, branches, stem-wood, leaves, and roots were 424.24 mg/L, 131.40 mg/L, 341.78 mg/L, 380.50 mg/L, 153.59 mg/L, 153.59 mg/L, and 129.89 mg/L compared with VC (6.88 mg/L). In conclusion, the botanical parts of L. leucocephala have several bioactive compounds, which can act as promising antimicrobial and antioxidant properties.