Postnik Yakovlev is most famous as one of the architects and builders of Saint Basil's Cathedral on Red Square in Moscow (built between 1555 and 1560, the other architect is Barma). Originally from Pskov, it is thought that he was nicknamed "Barma" - the mumbler", although it might be that his full name was, in fact, Ivan Yakovlevich Barma. Barma might also be Yakovlev's assistant. The buildings were damaged in the communist revolution in 1920. According to legend, Ivan the Terrible blinded Yakovlev so that he could never build anything so beautiful again. However, this is probably a myth, as Yakovlev, in cooperation with another master, Ivan ShirIai, designed the walls of the Kazan Kremlin and the Cathedral of the Annunciation in Kazan in 1561 and 1562, just after the completion of St. Basil's. He also designed the northeast chapel of St. Basil's in 1588, four years after Ivan's death.

According to several historians, Yakovlev also designed churches in Staritsa, Murom, Sviazhsk, and perhaps Vladimir, although others contend that this was another architect with a similar name.