Do I need two coats of paint if I use primer?

In most cases, yes, you still need two coats of paint even if you use primer, although primer significantly improves coverage and can sometimes make one coat sufficient in ideal conditions. Primer and paint serve different purposes. Primer is designed to seal porous surfaces like bare drywall or wood, provide a uniform base, improve adhesion, and block stains or dark colors from bleeding through, but it is not designed to provide final color richness, sheen uniformity, or long-term durability. The topcoat provides the actual color, sheen, washability, and protection. Even with primer, one coat of paint often looks uneven, slightly translucent, or patchy, especially with lighter colors over white primer, and it may not achieve the full depth of color or the intended sheen. Two coats of topcoat ensure even coverage, true color, proper film thickness for durability, and a consistent finish. The exception is when you are repainting the same or very similar color over a previously painted surface in good condition with a high-quality paint that has excellent hide, then primer plus one coat might be enough. However, for best results, professionals almost always apply primer plus two finish coats.