Prior was born in London to a British father and a Russian mother who descended from Constantin Stanislavski. Prior began composing at the age of eight and has written more than 40 works, including symphonies, concertos, two ballets, two operas, and a Requiem for the children of Beslan. At an early age, he began piano lessons. He later enrolled in the junior department of the Royal College of Music. At 13, he entered the Saint Petersburg Conservatory where, beginning in his third year, he studied composition with Boris Tishchenko and opera and symphonic conducting with Alexander Alexeev (a pupil of Hans Swarowsky). In 2009, at age 17, he graduated with Distinction two Masters-Degrees in Symphonic and Operatic Conducting, and in Composition from the St. Petersburg Conservatory.