Born on 15 March 1959 in Jordanów (Sucha Beskidzka district). Leśniakiewicz is a graduate of the Main School of Fire Service. In 1982, he was awarded the title of Fire Service Engineer, and in 1996 he graduated with a Master’s degree in firefighting. In addition, he graduated from postgraduate studies in technical rescue and emergency management. He participated in training courses in Poland and abroad, including courses organised by international training institutions. In 2015, he received an honorary doctorate from Lviv State University of Life Safety. 

Since 1982, he has served in Nowy Targ, and in 1984 was entrusted with the position of District Fire Service Chief. From 1992 to 1997 he served as district commander of the State Fire Service in Nowy Targ, then moved on to the position of the commander of the School of Aspirants of the State Fire Service in Kraków, where he worked until 2003. In 2003, he was appointed commander of the Mazovian Regional Fire Service, and two years later he became Deputy Chief Fire Service Commander and Deputy Chief of National Civil Defence.
From 2008 to 2015 he was Commander-in-Chief of the State Fire Service, and Chief of National Civil Defence. In 2016 he was discharged from the National Fire Service after 38 years of service.

He continues to participate in the life of the organisation by serving as Vice-President of the Management Board of the Association of Volunteer Fire Brigades of the Republic of Poland. In recent years, as an expert in crisis management and civil protection, he has organised exercises and conducted training sessions connected with the European Civil Protection Mechanism in Ukraine and Moldova, supporting the organisation of Volunteer Fire Brigades in the aforementioned countries and in Lithuania.