Isotope analysis suggests the majority of the former population bred in the Kazakh Steppe despite a record from the Siberian swamps, and was migratory, formerly wintering in shallow freshwater habitats around the Mediterranean.

This species has occurred as a vagrant in western Europe, the Canary Islands, the Azores, Oman, Canada, and Japan.

In November 2024, the species was declared globally extinct, with the last irrefutable sighting of the slender-billed curlew identified from Morocco in February 1995.

The juvenile plumage was very similar to the adult, but the flank were marked with brown streaking, the heart-shaped spots only appearing toward the end of the first winter.

The only confirmed breeding records of the slender-billed curlew were a small region of raised bogs north of Omsk, Russia in a period between 1909 and 1925.

Isotopic analysis suggests that main breeding range of the species was in a narrow belt in Kazakhstan centered around the 50th parallel north.

[5] In recent history, it mostly migrated to the Mediterranean as well as southern Arabia, with claims in the northern reaches of the Persian gulf, in Kuwait and Iraq.

After a long period of steady decline, the slender-billed curlew became extremely rare by the late 20th century, then thought to be fewer than 50 adult birds, with the last verified sighting from Morocco in 1995.

[9] The predicted breeding habitat of the bird in the Kazakh steppes was extensively transformed into wheat-growing farmland as part of the Soviet Virgin Lands campaign during the 1950s, which resulted in the decline of many bird species native to the area, and probably also affected the slender-billed curlew, though the population decline for the species appears to have begun decades before the farming campaign.