This small Nearctic sandpiper migrates from its principal breeding ground in the Canadian Arctic to the southern extremities of South America, one of the longest animal migrations in the Western Hemisphere. Much of its migration is made in a few, long, non-stop flights, each of which can last as long as 60 hours and transport these birds up to 4,000 kilometers, powered by extensive body fat. Such fat reserves are laid down at key migration staging areas—wetlands where food is especially abundant—making this bird particularly vulnerable to loss of strategic habitat. Southbound migrants fly over the Atlantic Ocean from northeastern North America to northern South America, and then gradually move southeast along the coast before turning inland in trans-Amazonian travel of about one month. Northward migration from Patagonia is apparently similar, at least through South America; the birds then move across the Caribbean and through interior North America to arctic breeding grounds.

As a breeder, the White-rumped Sandpiper occupies wet, hummock-tundra near marshy ponds, nesting on the ground and laying four, distinctive, pale to olive green eggs, spotted with reddish-brown. It performs elaborate courtship and territorial displays, and is vocal near its nest. It usually forages in small groups, but individuals also defend feeding territories.

This species associates freely with other sandpipers; its highly visible white patch behind the rump and distinct call are its best field characters.