Oxidoreductase that catalyzes the last step in proline biosynthesis, which corresponds to the reduction of pyrroline-5- carboxylate (P5C) to L-proline using NAD(P)H (PubMed:23024808, PubMed:36414121). Proline is synthesized from either glutamate or ornithine; both are converted to P5C, and then to proline via pyrroline-5-carboxylate reductases (PYCRs) (PubMed:23024808). PYCR3 is exclusively linked to the biosynthesis of proline from ornithine (PubMed:23024808). {ECO:0000269|PubMed:23024808, ECO:0000269|PubMed:36414121}. This is the function of PYCR3 (pyrroline-5-carboxylate reductase 3, Ensembl gene identifier ENSG00000104524).