As the cornerstones of societies, teachers play crucial roles in which society can build and shape an inclusive, equitable, and quality education system (Lawrie, 2013a). Stemming from the research that has established strong connections between teacher quality and student success (Darling-Hammond, 2000; Guskey & Sparks, 2004), also highlighted the significance of understanding more about quality teacher professional learning. However, Bangladesh, a developing country with a population of 180 million and a total of over 0.6 million teacher population [Bangladesh Bureau of Educational Information and Statistics (BANBEIS), 2022], has shortage of teachers as well as a dearth of research and limited emphasis on teachers' voices regarding their professional learning (Batra, 2005b; Roshid, Siddique et al., 2015). This research utilized a qualitative design to delve into and attain a deeper understanding of lived experiences of secondary school teachers in Bangladesh, through their participations in professional development programs. The objective is not merely to categorize but to unearth layers of understanding that underlined these teachers' experiences and perceptions. Drawing a total of nine secondary-level in-service teachers from the three main school types; government, non-government, and madrassa (Islamic religious school) in Bangladesh, this research tries to capture these teachers' personal accounts of in-service professional development experiences (Lawrie, 2013b). Thus, this research sheds light on the unique characteristics and components of teacher professional development in Bangladesh while identifying similarities with research conducted in Western contexts. Existing research has found that teacher professional development programs often lack effectiveness and are perceived as irrelevant by teachers (Opfer & Pedder, 2011b). Hence, this research explores the perceived impact of professional development experiences provided to secondary teachers in developing countries like Bangladesh and countries with similar socio-economic and educational contexts. Through in-depth semi-structured interviews conducted virtually, this research uncovers how teachers describe the essence of their lived experiences concerning in-service professional development programs, how these experiences influence their professional growth as teachers, and their perceptions of the impact of professional development on their student learning outcomes. The findings of this qualitative research contribute to the existing body of knowledge on teacher professional development, particularly within the context of Bangladesh. Furthermore, the insights gained from this study inform future policies, practices, and collaborations among stakeholders to design, curate, and implement more effective and contextually relevant teacher professional development initiatives. This research also lays a foundation for further investigations in teacher education and professional development field in Bangladesh. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]