He was born, like his younger sister, at São Paulo de Luanda, Angola, where his father was the Governor and Captain General, and was named after King Miguel of Portugal and both his paternal grandfather and paternal uncle. Because of the Letter of Law of 19 May 1863 that came to abolish all the Majorats and Chapels he was co-heir of his parents and all of his father's several former Majorats and House or Paço of os Arcos, all in Santa Comba Dão, Santa Comba Dão, with his sister, who was unmarried and had no children and lived with her brother. He was a fidalgoknight of the Royal Household by succession and a Bachelor graduated in Law from the University of Coimbra. He was 2nd Baron of Santa Comba Dão by Decree of Luís I of Portugal.
Maria Ludovina de Sousa Horta, married on 29 August 1880/1881 António Osório Sarmento de Figueiredo, Jr., and had issue
He married secondly Maria da Glória da Costa Brandão e Albuquerque, daughter of António José da Costa Brandão de Brito de Mesquita Vaz Velho Castelo-Branco, Captain-Major of Oliveirinha, Fidalgo of the Royal Household, etc., and second wife, distant cousin, goddaughter, sister in law and godmother Teresa Augusta de Albuquerque Pinto Tavares Castelo-Branco, and sister of the 1stViscount of Ervedal da Beira, and had eight children:
* Maria Susana Monteiro Gomes Horta e Costa, married on 1 November 1913 Carlos Duarte Mascarenhas de Meneses, CavalryOfficerMajor, with the Course of the Arm, etc., only son of Tomás Eugénio Mascarenhas de Meneses and first wife Sofia de Freitas, and had issue, one daughter
* Maria da Glória Monteiro Gomes Horta e Costa, married firstly on 4 December 1909 Dr. Francisco de Paula de Carvalho Vale e Vasconcelos, Medic, etc., and had issue, one son, and married secondly on 23 November 1915 Eduardo Francisco de Azeredo e Vasconcelos, First Lieutenant of MaritimeAviation, etc., and had issue, one son
* Octávio Maria de Oliveira, married in Cascais on 19 April 1934 Maria Luísa Ramil Saldanha, only legitimate daughter of Luís Carlos de Leão Saldanha and Maria José de Almeida Ramil, without issue
Maria da Conceição de Sousa Horta e Costa, married José da Costa Henriques, Teacher of the Ordinary Superior School of Coimbra, etc., and had issue
Diogo Maria de Sousa Horta e Costa, Superior Official and 1st Official of the Ministry of Public Instruction, etc., married Cristina Pedreira de Lima, by whom he had had one son, and had a recognized son:
* Diogo Luís de Sousa Horta or Diogo Luís de Lima Horta e Costa, Licentiate in Medicine, married German Annelise Marie Stuhlmacher, and had three children:
** Vera Maria Stuhlmacher Horta e Costa
** Diogo Frederico Stuhlmacher Horta e Costa
** Pedro Miguel Stuhlmacher Horta e Costa
* Luís Diogo de Sousa Lopes e Horta or Lopes de Sousa Horta or Luís Diogo Horta e Costa, Licentiate in Medicine from the University of Lisbon, Stomatologist, married on 22 July 1948 Maria Isabel Pizarro Xavier Montalvão Machado, daughter of Dr. José Timóteo Montalvão Machado, Licentiate in Medicine from the University of Lisbon, specialized in Ophthalmology from the University of Paris, etc., Secretary General of the Associação dos Arqueólogos Portugueses, Genealogist, etc., and Maria Leonor Pizarro Xavier, and had three daughters:
** Leonor Maria Montalvão Horta e Costa married Luís Filipe Serra Matias and had one children: *Mariana Montalvão Horta e Costa Matias
** Maria José Montalvão Horta e Costa
** Maria de Lurdes Montalvão Horta e Costa married Arnaud Max Marcel René Lantoine and had one children: *Alain José Montalvão Horta e Costa Lantoine
