The Mexican Democratic Party (Spanish: Partido Demócrata Mexicano, PDM, also known as El Partido Gallito Colorado, "The Little Red Rooster Party") was a Catholic social conservative political party in Mexico that existed between 1979 and 1997. At its height in 1982, the party had over 500,000 active voters and 12 seats in the Mexican Chamber of Deputies (Cámara de Diputados).

The Mexican Democratic Party (PDM) traces its origins to the Manuel Torres Bueno faction of the National Synarchist Union (UNS), a right-wing Catholic and clerical fascist organization. The UNS was founded in 1937 to oppose the anti-Catholic articles of the 1917 Constitution and the secular policies of President Lázaro Cárdenas. Its activities gained significant traction in regions such as Jalisco, Aguascalientes, Querétaro, Guanajuato, and Michoacán—areas that were central to the Cristero War (1926–1929).

Although the UNS declined after the 1940s, it remained influential in local politics, particularly in the Bajío region, known for its strong Catholic traditions. By the 1970s, the UNS experienced a revival due to electoral reforms introducing proportional representation, which allowed smaller political groups to participate in elections. During this period, Catholic organizations such as Opus Dei gained prominence in Mexican society, advocating for greater Catholic influence in politics and education. This cultural and ideological resurgence contributed to the creation of the Mexican Democratic Party (PDM) on June 15, 1975, in Mexico City.

The Mexican Democratic Party was established by former members of the UNS, National Action Party and other right-wing organizations with the goal of creating a pluralistic and democratic society rooted in Catholic values. Key figures, such as Ignacio González Gollaz, were instrumental in its founding and leadership. The PDM sought to formally engage in electoral politics to challenge the dominance of the Institutional Revolutionary Party (PRI) and provide a platform for Catholic conservatives, particularly in rural communities.

Initially, the PDM concentrated on building its support base in the Bajío region, which had historically supported the UNS. This stronghold allowed the party to organize and promote its vision of a society guided by Christian-social principles and rooted in traditional values. By 1979, the PDM achieved official recognition as a political party, marking its entry into national elections and formal politics.

In the 1979 legislative elections, the PDM gained 10 seats in the Chamber of Deputies. It increased its representation to 12 seats in the 1982 election. It was in the old UNS heartlands that the PDM obtained its greatest electoral presence, prevailing in several important municipalities like Lagos de Moreno in Jalisco or the city of Guanajuato.

Although the PDM managed to gain seats in the Chamber of Deputies, it was a very small opposition party compared to the PAN, having gained only 2.3% of the nationwide vote during the 1982 general election. Even so, if its seat increase from the 1979 congressional election to the 1982 election is considered, the PDM had the second-highest (after the PAN) percentage increase of total votes out of all the political parties in Mexico.

Up until the presidential elections of 1988 the party experienced internal divisions that contributed to its decline.^{[AI-retrieved source]}