Poly (ADP-ribose) polymerase-1 (PARP1) is involved in DNA repair, its inhibition can potentiate cell killing by different agents. When used in conjunction, inhibitors of PARP1 can sensitize the action of chemotherapeutic agents thus making PARP1 an attractive target for therapeutic intervention in cancer. Docking of 9-phenyl acridine (ACPH) with human PARP1 (hPARP1) revealed that ACPH could bind by interacting with the catalytically important amino acids at its NAD+ binding pocket. Its binding free energy was also determined to compare with that of other known inhibitors. Molecular dynamic simulation also established the binding of ACPH at the NAD+ binding pocket and also revealed its interaction with the catalytically important residues. These findings indicated that ACPH can be a potent hPARP1 inhibitor. In cultured A375 cells, post treatment with ACPH could sensitize cells to killing in both exponential and quiescent cells. NAD+ is the substrate for hPARP1 in DNA damaged cells; hence depletion of NAD+ indicates hPARP1 activity. The NAD+ content of treated cells were determined biochemically. Post treatment with ACPH prevented NAD+ depletion in the DNA damaged cells confirming its hPARP1 inhibitory activity. Considering the significance of hPARP1 inhibitors not only in cancer therapeutics but in various pathological conditions, the findings could be noteworthy for new drug development.