Svetoslav Gavriiski was born in Svishtov on 18 December 1948.
He finished high school in Sofia, 1967.
In 1972 he received a university degree in foreign trade relations from the Karl Marx Higher Institute of Economics, Sofia.
In 1972 he began work as economist with the Foreign Trade Office of the Ministry of Finance, joining the Currency and Finances Department in 1977.
In 1988 he became a chief expert for the Ministry of Economy and Planning, the National Balances Department.
In 1990 he was appointed chief expert at the International Finances Department of the Finance Ministry.
In the period 1991 - 1992 he served as chief of the Foreign Finances Office and in 1992 - 1997 he held the post of Deputy Minister of Finance.
Gavriisski was member of the Bulgarian team participating in the talks with the London Club of private creditor banks on the extension and renegotiation of  Bulgaria's external debt.
In February-May 1997 he held the office of Minister of Finance of the Stefan Sofiyanski caretaker government.
He took part in the drafting of the new Bulgarian National Bank Law by which, effective of 1 July 1997, a monetary system based on the principles of the currency board was introduced in Bulgaria.
On 11 June 1997, the 38th National Assembly elected him Governor of the Bulgarian National Bank.
In October 2005 his candidature for mayor of Sofia was put forward by the Democrats for Strong Bulgaria (Ivan Kostov). He failed to reach the runoff but nevertheless gained support and ranked third after Boyko Borisov (independent) and Tatyana Doncheva (BSP).
2006 - member of the Board of Management of Allianz Bank Bulgaria. Chief Executive Director of Allianz Bank Bulgaria.