The present study was carried out with the aim to isolate an antibacterial pigment from seaweed-associated bacterium. The bacterium was identified as Halolactibacillus alkaliphilus MSRD1 by 16S rRNA sequencing. The isolated bacterium was cultured in 50% Luria-Bertani seawater broth (LB-SWB) with 1% glycerol. The pigment was extracted with 99% ethanol and analyzed by UV-Vis spectroscopy at 490 nm. The candidate bacterium was optimized with various NaCl concentrations from 5 to 20%. The results inferred that the bacterium produce maximum pigment at 5% NaCl level. The candidate bacterium H. alkaliphilus MSRD1 was found to be producing the maximum pigment during the 120-h incubation. The protein content of the pigment was found to be maximum of 72% at the end of the 120-h incubation. The extracted pigment was stable up to 80 °C, pink at acidic pH (1 to 5) and orange at basic pH (8 to 12). The isolated pigment was fractionated by silica gel column chromatography. Fractionated pigment was characterized by TLC, FT-IR, and SDS-PAGE. In the antibacterial context, the pigment was highly inhibited Staphylococcus aureus and Salmonella typhi with the zone of inhibition 16 and 14 mm, respectively. According to SDS-PAGE, the size of the pigment was approximately 80 kDa. The H. alkaliphilus MSRD1 has high capacity to produce the pigment with antibacterial properties. This could be effectively used in the future.