Harald Aars (31 May 1875 – 4 June 1945 (aged 70)) was a Norwegian architect.
He was born in Christiania as a son of educator Jacob Jonathan Aars (1837–1908) and his wife Anna Ernesta Birch-Reichenwald (1838–1919). He was the brother of academic Kristian Aars, a grandson of Christian Birch-Reichenwald and a great-grandson of Peter Motzfeldt. He was also a grandnephew of priest and politician Jens Aars and a second cousin of writer Sophus Christian Munk Aars. In 1899 he married Anna Dybwad Berentzen (1878–1947), a maternal granddaughter of Jacob Dybwad.
Aars finished middle school in 1890, and worked one year at Thunes Mekaniske Værksted before enrolling at construction engineering at Kristiania Technical School. He graduated in 1895, and studied architecture at the Royal College of Arts from 1897 to 1898. During this period he picked up inspiration from William Morris, Walter Crane, C. R. Ashbee, the Art Workers Guild and the Arts and Crafts Movement. He later stayed in the United Kingdom and France from 1901 to 1902, and also had stays in Italy and Greece.
In Norway he was an assistant of Holger Sinding-Larsen from 1899 to 1901 and for the city architect of Kristiania from 1902 to 1904. From 1904 to 1919 he had his own architect's office. He worked with Harald Hals og Lorentz Harboe Ree, especially from 1915. Most of his buildings were raised in the districts of Frogner, St. Hanshaugen and Bislett. A common style, especially around 1920, was the "Nordic neo-baroque". From 1920 to 1940 he was the city architect of Kristiania/Oslo. In this position he was especially responsible for construction of schools.