He participated in the Great Northern War and for sometime performed duties of military commandant of Poltava city.
On 19 April 1722 as a brigadier he was appointed the president of the new Collegium of Little Russia (confirmed by the manifest of Emperor Peter the Great on 16 May 1722).
Velyaminov prepared number of drafts about reformation of the system of power relations of the Cossack Hetmanate that in 1723 became a basis of legislative acts of Peter the Great and the Governing Senate.
As the result of their realization, Velyaminov took over the functions of the Ukrainian Governor, subjected the Cossacks' General Military Chancellery and the local government.
For success reached in reformation of the Hetmanate administrative system, Velyaminov was awarded a rank of Major General by Catherine I on 11 July 1726.