In 1979, she finished middle school (pre-university) with a degree as Educator in Child Day-Care Centers, which reinforced her professional vocation towards pre-school teaching.

In 1983, she graduated from the Pedagogical University of Havana with specialty in Pedagogy-Psychology. That same year she started to work in the Department of Pre-school Education as principal teacher of Pre-school Psychology. She taught different subjects of the Pre-school Education curriculum: Teaching resources, Methodology for Music and Dance Education, Methodology for Teaching Pre-school Psychology, Pre-school Pedagogy, Sexual Education (principal teacher), and Psychological bases of Child Sexual Education (principal teacher), among others. She joined the Education Television Laboratory (1983-1990) and participated in documentaries with original ideas, scripts, research and advice (some of them have received awards).

At this University, she developed her research, mainly in the field of Child Educational Psychology, from the theoretical-methodological conception of the Historical-Cultural School of Lev Vygotski. With this approach she began research and postgraduate education in the field of sexual education. She introduced sexual education in her teaching activities. Since its beginning in 1976, she was part of the Research Group on Sexual Education, which later became the Sexuality and Sexual Education Cathedra.

In 1990, she began her education in the field of social psychoanalysis and in 1994 she attained the degree of Specialist in Community Intervention, centered on daily-life Corrective Processes (ProCC, Spanish acronym), at the Marie Langer Community Health Development Center  in Madrid, Spain. Essentially, she has used this education as a methodological resource in teaching, research, community work, promotion of sex rights and the creation of a cartoon series: Puberty.

In 1997, she became Master in Sexuality, at the National Center for Sexual Education and the Higher Institute of Medical Sciences of Havana. As part of her thesis she prepared and developed the Program of Education and Qualitative Research: Growing in Adolescence. As a result of this experience she wrote the book What happens to us in Puberty? edited in Cuba, Italy, Croatia, Portugal, Argentina, Mexico and the Dominican Republic. In Cuba, a Braille version was made.

In 1990, Mariela Castro started to work as specialist at the National Center for Sexual Education (CENESEX, Spanish acronym) and has remained Adjunct Associate Professor at the Enrique José Varona University of Pedagogical Sciences. From CENESEX, she presented a proposal for Sexual Education Program for pre-school educational institutions (infant day-care centers) to the Ministry of Education of Cuba; the Sexual Education Program for the art schools (presently in use) to the Ministry of Culture; organized the system of CENESEX postgraduate education in Sexology and Sexual Education and cathedras in all Medical Sciences Universities throughout the country and introduced community work as one of the development profiles of CENESEX. She has taught in numerous postgraduate courses, diplomas, masters at the CENESEX and other institutions and universities in Cuba and other countries.

Mariela Castro is one of the founders of the journal Sexología y Sociedad (1994), unique of its type in Cuba, and from that date forms part of the Editorial Council. She pressed for the creation of the National Program of Planned Parenthood, approved by the Ministry of Public Health in 1993, participated in its preparation and in the organization of the commission in charge of it, as well as in the preparation and drafting of the National Program of Integral Health Care for Adolescents.

She was member of the Technical Advisory Council of the Latin American Reference Center for Pre-school Education (CELEP, Spanish acronym), coordinator and professor of the Academic Committee of the Sexuality Master and professor of the Academic Committee of the Master “Community Intervention in the Corrective Processes of Daily Life”, both of CENESEX.

In 2000, she became director of the CENESEX and the journal Sexología y Sociedad. Since then, she is president of the CENESEX Scientific Council and of the Cuban Multidisciplinary Society for the Study of Sexuality (SOCUMES, Spanish acronym) from 2000 to 2010.

In 2004, she prepared an education strategy for the Integral Attention of Transsexual People, for its inclusion in the public policies. Since then, it constitutes the main research topic to press for legal, educational, media and health initiatives, among others, with the purpose of promoting respect to the rights and full dignity of trans people and their just social integration. Thanks to this initiative, a resolution of the Ministry of Public Health was issued in May, 2008, which legitimizes specialized health care for transsexual people, including surgery for sex reassignment, as a free service of the Public Health System. She has also participated in the preparation and promotion of modifications to the Family Code that include, among other benefits for Cuban families, respect for free sexual orientation and gender identity and legal recognition for same sex couples. She is president of the National Commission for the Integral Attention to Transsexual People, since 2005.

She also coordinates the educational strategy and the public benefit campaign to promote respect for free sexual orientation and gender identity, including the celebration throughout the country of the Activities for the International Day against Homophobia; activity she presides since 2007.

Her education in the ProCC methodology was used in a cartoon series called Puberty, where she contributed the original idea, narratives, script and advice. The series has received seven international awards, among them the Iberoamerican Prix Jeunesse 2011, as well as two prizes in the international cartoon festival in Italy (Pulcinella, 2009) and in Argentina (Nueva Mirada, 2009, Sección Mi TV). In the Havana Book and Reading Festival, 2012, she was awarded the Silver Medal for the most sold title with the new edition of the book What happens to us in Puberty? She participated in the 11^th Havana Biennial as curator of the collateral exhibition Travesías (Voyages). This exhibit aimed at sensitizing the public with the vicissitudes of people, whose sexual orientations do not subject to the hetero-standards imposed by patriarchal domination models.

She has more than ten books published in Cuba and other countries, translated into different languages and more than 20 scientific articles published in scientific and academically renowned journals.

Having participated in over one hundred national or international scientific congresses as speaker and/or organizer (president, vice-president or member of organizing and scientific committees), she was the President of the 16^th World Sexology Congress held in Havana in 2003 and member of the international scientific committees of the WAS congresses carried out every two years.

During her professional career she has been awarded several prizes, distinctions and recognitions, among them: Premio “Memoria”, 2005, given by the Pablo de la Torriente Brau Cultural Center; Public Service Award, 2009, by the North American Society for the Scientific Study of Sexuality;  Eureka Prize, 2012, for Scientific Excellency, awarded by the World Council of University Academics (COMAU, Spanish acronym); Premio Muestra-T, awarded each year to the person or institution whose professional path stood out for its commitment to the demands and struggles of the LGBT movement, international award of which only one is given each year. She received the CQGL Pris 2012, awarded by the Conseil Québécois LGBT, Canada; Diploma of recognition for outstanding work in favor of Sexual Education awarded in 2011 by the Marta Abreu Central University in Las Villas, Cuba, Recognition for outstanding and commendable work in favor of gender identity as an exercise of equity and social justice, Santiago de Cuba, May 2011; recognition for the contributions to the development of Sexuality Education at CAGSES during more than 15 years, Enrique José Varona University of Pedagogical Sciences , Havana, Cuba, 2012; Scientific Merit Diploma of the Manuel Fajardo Faculty of Medical Sciences and the Santiago de Cuba University of Medical Sciences, in recognition for relevant work in scientific development,  2012; and the title of Illustrious Visitor of Montevideo on August 2013 among others.

Since 2012, she is one of the 25 high-level personalities of the UN work group for the International Conference on Population and Development and the Millennium Development Goals. Her work has deserved recognition in different scientific and social scenarios and national and international institutions.

At present, she is member of the Latin American Association of Researchers on Human Reproduction (ALIRH, Spanish acronym) and the World Professional Association for Transgender Health; is member of the Advisory Committee of the World Association for Sexual Health (WASH), 2005-2013; Advisory Committee of IDAHO (International Day Against Homophobia) and the National Committee of the Federation of Cuban Women (FMC, Spanish acronym), feminist organization of the civil society, since March 2009. She formed part of the Aponte Commission of the Cuban Union of Writers and Artists (UNEAC, Spanish acronym) against racism and racial discrimination. She is member of the Cuban Society of Psychologists and SOCUMES. Since 2012, she is member of the Latin American Studies Association (LASA) and WPATH and also integrates the advising committee of the digital journal Salud Vida*).

In the 2013 general elections, she was elected member of the National Assembly of the Popular Power.