Hakob Kojoyan assisted Armenian architect Alexander Tamanian in creating the coat of arms for the First Republic of Armenia.

In Europe, he not only explored the remarkable collections of the past, but also witnessed for the creation of new paintings that have a significant influence on him to become an artist.

After the establishment of Soviet rule in Armenia in 1920 Kojoyan, along with several other Armenian artists, was involved in the art department of "Haykavrosta" and had created agitation-propagandistic posters, caricatures, and so on according to the sample of the "ROSTA Window" (Moscow).

In 1939 Kojoyan participated in a ten-day exhibition of Armenian art in Moscow and was awarded the Order of the Red Banner of Labour, meanwhile he received the title of People's Artist of the Republic.

In 1945 with the endeavours of Ara Sargsyan, the Institute of Fine Arts was opened in Yerevan with the Faculty of Painting and Sculpture, where Kojoyan worked as a professor.

[2] In 1973 the two-storey private residence of sculptor Ara Sargsyan and painter Hakob Kojoyan where they lived since 1934 started to operate as house-museum for 2 artists.