This work presents a complete investigation on the excited-state absorption of a new porphyrin derivative, the free-base 5,10,15,20-tetrakis (1,3-dimethylimidazolium-2-yl) porphyrin tetraiodide (H2-TDMImP), for which the excited singlet and triplet transient absorption spectra were obtained. In order to accomplish this task, we employed the laser flash photolysis (LFP) technique in association with the white-light continuum (WLC) Z-scan measurements. The transient singlet absorption spectrum shows a reverse saturable absorption around the Q-band region (500–650 nm) and a small saturable absorption around 650 nm. From LFP experiments we verified that this porphyrin presents a biexponential decay profile, with a low quantum yield for triplet state formation. Besides, we observed that the reverse saturable absorption also takes place in triplet state.