After receiving his basic education in the Nuremberg public schools, he attended the Academy of Fine Arts there. Although he began as a painter, he was soon attracted to engraving and began formal studies with Samuel Amsler. At first, he concentrated on small plates for book publishers but, even then, his mature pictorial style became apparent. Eventually, in 1866, on recommendation by Julius Thaeter (1804–1870), he was appointed to succeed the latter as Professor of Engraving at the Academy of Fine Arts, Munich.
He retired in 1895 and, with three of his friends, opened a painting studio.
Raab's works can be found in several museums, including the Alte Pinakothek in Munich.
His daughter Doris Raab was born in Nuremberg in 1851 and she became his pupil exhibiting in France and Germany. Doris Raab exhibited her work at the Palace of Fine Arts at the 1893 World's Columbian Exposition in Chicago, Illinois.