Addadi was born in Dély Ibrahim, Algiers, the son of Amar and Salima Addadi. Coming from an athletic pedigree, he started his sporting career at the age of nine. Recreationally, he swam with his brother in the local pool across the city's suburbs, until a prominent coach spotted and later asked them to join the national team. Ten years later, in 1997, Addadi left his homeland Algeria to move to the United States, where he received a full scholarship to attend Bolles School in Jacksonville, Florida. Fluent only in Arabic and French, he credited Bolles as a primary institution to learn English, and also, a training ground to prepare for college career. During his short stay, Addadi trained under Gregg Troy, a coach who produced numerous top-class swimmers including Ryan Lochte. Addadi attended the University of Maryland, Baltimore County in Baltimore, Maryland, where he played for the UMBC Retrievers swimming and diving team under head coach Chad Cradock. Serving as the team captain, he held the school's records in the 100-yard backstroke, 200-yard backstroke, and 100-yard butterfly, and later became a prizewinner of four different records in both freestyle and medley relays. In his senior season, Addadi was named the Most Outstanding Swimmer of the Year at the Eastern College Athletic Conference Championships after breaking a school record in the 100-yard butterfly. In the spring of 2002, Addadi graduated from the University with a bachelor's degree in financial economics.
International career
In 1999, Addadi attended the All-Africa Games in Johannesburg, South Africa. He broke the host nation's stranglehold after winning the 100 m backstroke title in 58.28, edging out Seychelles' Benjamin Lo-Pinto by almost a full body length. He also added a bronze to his hardware in the 100 m butterfly at 56.30, finishing just outside a top two finish from the South Africans. At the 2000 Summer Olympics in Sydney, Addadi competed only in two individual events for Algeria, along with Salim Iles. After collecting two medals from the All-Africa Games, his entry times of 58.28 and 56.30 were both officially accredited under a FINA B-standard. On the second day of the Games, Addadi placed forty-sixth in the 100 m backstroke. Swimming in heat two, he raced to a sixth seed in 58.74, just a 1.62-second deficit off a winning time set by South Korea's Sung Min. Five days later, in the 100 m butterfly, Addadi challenged seven other swimmers in the same heat, including Guam's 28-year-old Daniel O'Keeffe and Bosnia's three-time Olympian Janko Gojković. He held off a fast-pacing O'Keeffe by a hundredth of a second to snatch a third spot and forty-fourth overall in an Algerian record of 56.04.
