The study of the language of political communication has recently become one of the topical issues in humanities research. Much attention is paid to the study of the peculiarities of the linguistic means of political discourse at the lexical, grammatical, stylistic level. However, the problem of idiomaticity of political discourse has not been sufficiently covered. The purpose of this study is to identify and describe functioning of idiomatic speech units in political communication by the example of the English pre-election discourse. The paper gives a definition of idiomaticity, outlines the main approaches to the interpretation of this phenomenon, analyzes the central subgenres of the pre-election discourse from the point of view of idiomaticity - pre-election speech, pre-election television debates and interviews of politicians. It was revealed that idiomatic speech units represented by phraseological units are of the highest frequency in these subgenres. Structural and semantic types of phraseological units functioning in the analyzed discourse are determined, among which we identify non-predicative phraseological units (with the structure of a phrase), partially predicative (phrases with a grammatically leading component) and predicative ones, represented by proverbs. It has been determined that, in accordance with the ranking by frequency, non-predicative phraseological units are in the foreground. Their semantics is distinguished by a rather transparent connection with the motivating basis. The article provides excerpts from the above subgenres of the pre-election discourse, which makes it possible to show the significant role of idiomatic speech units in creating a political portrait of a politician, as well as in implementing communication strategies and tactics used by the participants of election campaigns. The research has theoretical and practical significance. In theoretical terms, the results obtained and the conclusions drawn can contribute to the further development of the theory of political discourse. The practical significance of the research lies in the opportunity of using its results in lecture courses on political linguistics, as well as in the development of methodological models for teaching translation and use of idiomatic speech units of English political discourse to students specializing in the field of international relations.