Activated carbons (ACs) were synthesized from golden shower (GS) through chemical activation. Two synthesis processes were used: one-stage and two-stage processes. In the one-stage process, GS that was impregnated with K2CO3 was directly pyrolyzed (GSAC), and the two-stage process consisted of (1) pyrolytic or hydrolytic carbonization to produce biochar or hydrochar and (2) subsequent chemical activation was defined as GSBAC and GSHAC, respectively. The activated carbon’s characteristics—thermal stability and textural, physicochemical, structural, and crystal properties—were thoroughly investigated. Results demonstrated that the characteristics of activated carbons strongly depend on the method used for their synthesis. The Brunauer–Emmett–Teller surface area followed the order GSAC (1413 m2/g) > GSHAC (1238 m2/g) > GSBAC (812 m2/g). The existence of acidic groups was determined through Fourier transform infrared spectroscopy and Boehm titration. The excellent adsorptive capacities of the activated carbons were confirmed from the iodine number (1568–2695 mg/g) and methylene number (143–233 mg/g).