A donatary captain was a Portuguese colonial official to whom the Crown granted jurisdiction, rights and revenues over some colonial territory. The recipient of these grants was called a donatário (donatary), because he had been given the grant as a doação (donation) by the king, often as a reward for service.

The term also applied as the rank of the field officer that was in charge of a captaincy's territorial militia, called ordenanças in Portuguese, a military unit which existed from the 16th to the 19th centuries.

Due to the impossibility of exercising direct control and sovereignty over overseas territories, the captain-major was the channel by which the monarch could delegate his powers, with certain restrictions, under the responsibility of persons in whom he confided. The donatário could administer, on behalf of the Sovereign, the lands to which he was assigned, with all the regalia, rights and obligations, with the exception of certain limits, including military authority over soldiers and detachments of the crown, or the administration of justice.

The captains were agents nominated by the donatary or, after 1495, by the Portuguese Crown, to a lifetime title that was passed down to the "legitimate male heirs". As administrators, the captain-majors enjoyed various judicial and economic privileges that provided an incentive to settle and develop their captaincies. They had the authority to administer sentences, with the exception of those involving penalties of death or mutilation. Economically, they had the exclusive authority to mill, bake bread and sell salt, in addition to their entitlement to receive rent paid to the King for lands, fees and due taxes. In addition, they could receive a tithe paid to the captaincy directly. In addition to the regalia of office, the captains-major were entitled to the best parcels of land, and had the capability, on behalf of the Crown, to contract renters to the donatárias (that is, the lands of the donataries). Most donatary titles were hereditary, with a few exceptions mentioned in the Salic laws (Portuguese: leis Sálicas) of the time, which regulated all aspects of life, including crime, taxation, indemnity, and female inheritance; captains-major were less restricted to these conditions.

Many of these captains were selected as part of a consolidation of relationships between the donataries and their vassals. This subjective process usually involved close associations with the royal family or confidants of the Crown: a feudal meritocracy of vassals. This could result from rendering service during the overseas expansion, or from some heroism deemed as worthy of entitlement. The monarch surrounded himself with men seen as trustworthy, those who were already socially close to him, forming a restricted circle of individuals. In some cases, precedents were superseded in favor of persons in whom they could trust, including setting aside the laws of male inheritance in favor of a heiress, for example—as in the case of Antonia, Jácome de Bruges's daughter. Yet, most had to prove themselves, and those who did not succeed in proving their worth could lose their rights, as happened to Álvaro de Ornelas, captain of Pico, who lost his captaincy due to the perceived inefficiency of its settlement.

The captaincy system was built on confidence and good faith between the captain and the donatário, owing to the distance between them. This weakened the donatary's control over the officials, resulting in a disparity between actual and perceived functions. Some were either incompetent in their roles, power-hungry, or just absent. In some cases, the inhabitants of certain possessions were often subject to irregularities resulting from judicial or fiscal issues. Some captains appointed overseers, called ouvidores (lit. 'hearers', or auditors) to represent those who were unqualified to respond to the issues of their masters.

The following is an incomplete list of some of the captaincies and their first donatary captains.

There were three captaincies in the archipelago of Madeira, associated with the three principal discoverers of the islands: