In a governmental system, a party leader acts as the official representative of their political party, either to a legislature or to the electorate. Depending on the country, the individual colloquially referred to as the "leader" of a political party may officially be party chair, secretary, or the highest political office.

The party leader is often responsible for managing the party's relationship with the general public and leading the competition against political rivals, similar to the role of a party spokesperson. As such, they will take a leading role in developing and communicating party platforms to the electorate.

In many representative democracies, party leaders compete directly for high political office. It is thus typical in such states (notably in the Westminster system) for the party leader to seek election to the legislature and, if elected, to simultaneously serve as the party's parliamentary leader. In several countries utilizing the parliamentary system, if the party leader's political party emerges with a majority of seats in parliament after a general election, is the leading party in a coalition government, or (in some instances) is the largest party in a minority parliament, that party's leader often serves as the prime minister. Thus, in the politics of several countries utilizing the parliamentary system, a political party's leader is treated as a de facto candidate for prime minister by the media and the general public, even if said office is technically not directly elected.

Party Head or leader of a political party, subject to party's constitutional document need not be elected member of legislature and is therefore different from leader of parliamentary committee of a party.

This is much harder to do in presidential and semi-presidential systems, where the chief executive is a president who can only be removed by a special impeachment (typically involving a legislative supermajority, an investigation by a constitutional court, or both), and removal entails either a snap election or automatic succession to office by a vice president; therefore, the party's de jure internal leader either takes a background role (such as the Chairs of the Democratic, and Republican parties in the United States, who serve more so as the chief administrative officers of their respective political parties), or the leadership may be automatically bestowed on an incumbent president who belongs to the party (such as the Democratic Progressive Party in Taiwan). In countries using the Westminster system, the leader of the largest political party not within the government serves as the leader of the opposition.

In Canada, the leaders of all major political parties are chosen during their respective political party's leadership conventions upon the completion of a leadership election. Exceptions to this process sometimes occur when Members of Parliament leave their former party to form a new party; examples of this include when Jean-François Fortin quit the Bloc Québécois to form Strength in Democracy in 2014 and when Maxime Bernier quit the Conservative Party to form the People's Party of Canada in 2018.

The leaders of communist parties often hold the title of general secretary (e.g. General Secretary of the Communist Party of the Soviet Union and General Secretary of the Chinese Communist Party) and the officeholder is usually considered the paramount leader of China. On 15 November 2012, Xi Jinping was elected General Secretary of the Chinese Communist Party at the 18th Communist Party national congress.

The party organizations themselves and also their representatives (such as the chairperson, who is the party leader, and other board members) play a much more prominent role in German politics than they do in many other countries, where the parties are mainly represented by their members and leaders in government. Although the party leaders often also hold important public offices (such as government minister or parliamentary leader), those roles are clearly separated, even by law. Consequently, it does occasionally happen that the leaders of a German party are not even members of parliament, such as Saskia Esken and Lars Klingbeil, who are incumbent the chairpersons of the (governing) Social Democrats. This sometimes leads to open conflicts between the party leadership, its parliamentary group and its members of government.