He specialized in military logistics and transportation, focusing his work on the region between the Douro and Tagus rivers, as well as the roads and railways of Estremadura Province.

[1] Teles was involved in military education and training, serving as commandant of the Escola do Exército (School of the Army; Portugal's then war college).

One of his works, Introdução ao estudo dos conhecimentos militares ("Introduction to the study of military matters"), won the Lisbon Academy of Sciences' D. Luís I Prize.

[1] Having dedicated most of his career to military education, Teles did not enter politics until 1898, when he accepted the position of Minister of War in the government led by José Luciano de Castro, leader of the Progressive Party.

Teles served as Minister of War twice more: between 20 October 1904 and 27 December 1905 as part of another José Luciano de Castro government,[2] and between 4 February 1908 and 14 May 1909 under the successive governments led by Francisco Joaquim Ferreira do Amaral,[2][3][4] Artur Alberto de Campos Henriques,[2] and himself.

[2] His second and third tenures as minister took place in a time of increasing political instability following the assassination of King Carlos I of Portugal by republicans.

During a plenary session of the Cortes Gerais on 10 March 1909, Caeiro de Mata had accused Espregueira of fraud and other "criminal" activities for deciding to loan public money to the Companhia dos Caminhos de Ferro Portugueses [pt], a railway company to which Espregueira was linked.