Gustaaf Paul Robert Magnel (born 15 September 1889 in Essen (Belgium); died 5 July 1955 in Ghent) was a Belgian engineer and professor at Ghent University, known for his expertise regarding reinforced concrete and prestressed concrete.
After he returned to Belgium from the UK in 1919, he joined the Strength of Materials Laboratory at Ghent University.
The French Association des Ingénieurs Docteurs honoured Magnel with its Grande Médaille, and he received the Frank P. Brown Medal from the Franklin Institute of Philadelphia.
Further honours include Commander of the Yugoslavian St. Sava Order and Chevalier de la Légion d’Honneur.
Magnel supported Eugène Freyssinet during the foundation of the Fédération Internationale de la Précontrainte (FIP) and was its first vice-president.