In 1821, before the consummation of Mexico's independence, Alamán was a deputy to the Cádiz Cortes (the Spanish national parliament) for the province of Nueva Galicia, now Guanajuato, among other states, New Spain. Later in the same year Mexico won its independence from Spain. Alamán returned to Mexico and became one of the most influential politicians in the nascent country. He was a co-founder and lifelong member of the Mexican Conservative Party, and he consistently defended the centralist organization of Mexico. It is said that he was one of those behind the murder of independence hero Vicente Guerrero. Under the junta that governed Mexico after the fall of Iturbide, Alamán served from 1823 to 1825 in the powerful post of Minister of Interior and Exterior Relations (Ministro de Relaciones Interiores e Exteriores; the U.S. equivalent of this posting would encompass the combined functions of Secretary of State, Secretary of the Interior, and Attorney General). He was a member of the junta that briefly governed Mexico in 1829 after the Plan de Jalapa with the aim of installing Anastasio Bustamante as president.
Alamán returned to the post of Minister of Interior and Exterior Relations in 1830-1832 under the Bustamante government. It was in this capacity that he named Manuel Victoria governor of Alta California March 8, 1830. In October 1830, he created the Banco Nacional de Avío, the first bank in Mexico. The Banco Nacional de Avío provided Mexico with the financial infrastructure necessary for its burgeoning economy. During the same period Alamán negotiated a deal with the United States to the north fixing the national borders of the two nations which held right up to the time of the Mexican-American War. He also promoted colonizing the northern provinces in order to stave off U.S. expansionism.
After what he saw as the disaster of Texas independence from Mexico in 1836, Alamán largely retired from politics, though he continued to promote what he saw as the interests of the country by serving as Director de la Junta de Fomento de la Industria (Directorate for the Promotion of Industry) from 1839 until his death. For most of the 1840s, he devoted himself primarily to writing the history of Mexico from the perspective of a conservative. His three-volume work Disertaciones sobre la Historia de la Republica mexicana (Mexico, 1844-1849) and his five-volume Historia de México, desde los primeros movimientos que prepararon su independencia en el año de 1808, hasta la época presente (Mexico, 1849-1852), stand as the major intellectual productions of the Conservative Party in nineteenth-century Mexico, and the only histories produced by a Mexican author of his era to view the Spanish presence in his country favourably.
Among his more important actions are the creation of the Natural History Museum in Mexico City and the foundation of Mexico's General National Archive. The latter has been very important for learning about the historical events in Mexico and understanding the political processes of the Mexican Republic. He also founded and ran a mining company, established the first metal foundry in independent Mexico in 1825, administered the estates of the descendants of Hernán Cortés, and served as president of the Mexico City ayuntamiento (city council) in 1849.
Lucas Alamán returned to national public service in 1851, when Santa Anna reappointed him for the last time to the post of Minister of Relations, in which he served until his death from pneumonia on June 2, 1853.