Wilson's Phalaropes exhibit reverse sexual dimorphism, meaning the females are larger and more brightly colored than the males during the breeding season. Females in breeding plumage have a grey head and back with reddish sides and a conspicuous black stripe running from the bill through the eye and down the neck. Their throat and underparts are white. Males in breeding plumage are duller, with a more muted gray and white coloration, and lack the reddish hues of the female. Both sexes have a thin, straight bill and long legs. In non-breeding plumage, both males and females are pale gray above and white below.

Female Wilson's Phalarope (Breeding):
• Size: Larger than the male.
• Coloration: Grey head and back, reddish sides, black stripe from bill to neck, white throat and underparts.
• Distinctive Feature: The reddish sides and bold black stripe are prominent features.

Male Wilson's Phalarope (Breeding):
• Size: Smaller than the female.
• Coloration: Duller than the female, with gray and white plumage, lacking the reddish tones.
• Distinctive Feature: Muted colors and a less prominent dark neck stripe compared to the female.

Both Sexes (Non-breeding):
• Plumage: Pale gray above, white below, with a plain face.
• Other Features: Thin, straight bill, long legs, and a slender build.