This scientific article is devoted to an overview of the architectural activities of Karl Ludwig Engel in the capital of Finland. After the Russian Emperor Alexander I chose Helsinki, which was rather unsightly at that time, as the new capital of the Grand Duchy of Finland, the city's redevelopment began, the architect of which was the German Karl Ludwig Engel. He acted as a designer of more than twenty buildings, including the Church of St. Nicholas, the Boca House, the Senate building, etc. Imbued with sympathy for the architectural appearance of St. Petersburg during his repeated visits, he transferred to Helsinki many elements of St. Petersburg neoclassicism, which was firmly entrenched in the Finnish capital. Basically, Karl Ludwig Engel worked in the central area of the city, helping to transform the Senate Square into the most recognizable landmark in Helsinki.