Nitrogen-doped carbon nanodots (N@CDs) were prepared by hydrothermal processing of bovine serum albumin (Mw: 69,324 with 607 amino acids). A polyaniline (PANI-N@CDs) nanocomposite was then synthesized by ultrasonication and used to degrade Congo red (CR), methylene blue (MB), Rhodamine B (RhB), and crystal violet (CV) four common organic dyes. The PANI-N@CD nanocomposite simultaneously adsorbed and concentrated the dye from the bulk solution and degraded the adsorbed dye, resulting in a high rate of dye degradation. The combination of holes (h+), hydroxyl (OH•), and O2•− was involved in the N@CD-mediated photocatalytic degradation of the dyes. Under visible light illumination at neutral pH, the PANI-N@CDs were proven as an efficient adsorbent and photocatalyst for the complete degradation of CR within 20 min. MB and RhB were also degraded but required longer treatment times. These findings supported the design of remediation processes for such dyes and predicted their fate in the environment. The nanocomposite also exhibited antimicrobial activities against Gram-negative bacterium E. coli and Gram-positive bacterium S. aureus.