Kirill Yuryevich Lavrov was born on 15 September 1925, in Leningrad, USSR (now St. Petersburg, Russia). He was baptized by the Russian Orthodox Church of St. John the Divine in Lavrushinskoe Podvorie Monastery in Leningrad. Young Kirill Lavrov was brought up in Leningrad, in a family with deep roots in St. Petersburg society. He was fond of literature and theatre from his young age, and was exposed to a highly stimulating intellectual environment in his family. He was also a good sportsman: he took gymnastics, fencing, and was a member of the youth football (soccer) team at "Spartak" sports club in Leningrad.
His maternal grandmother, Olga Leonidovna Lykoshina, was related to writer Aleksandr Griboyedov and belonged to Polish Nobility. His grandfather, Sergei Vasilyevich Lavrov, was Director of Gymnasium of the Imperial Humanitarian Society in St. Petersburg; he emigrated to Belgrade after the Russian Revolution of 1917, and died there in 1934. Kirill Lavrov's paternal grandmother, Elizaveta Akimovna, refused to emigrate and stayed home in Petrograd with her children. In 1919, his father, Yuri Sergeevich Lavrov, became an actor at the Bolshoi Drama Theatre (BDT) in St. Petersburg where his stage costumes were designed by the legendary theatrical artist Alexandre Benois. His mother, Olga Ivanovna Gudim-Levkovich, was also an actress in Leningrad. Both Lavrov's parents worked together at various theaters in Leningrad, they married in 1924, in Leningrad.
In the 1930s Leningrad was shocked by a series of high-level political murders and Great Purges under the leadership of Joseph Stalin. In 1934, the popular governor of Leningrad, Sergei Kirov was brutally murdered in his office. Joseph Stalin targeted Leningrad for the purpose of degrading the superior reputation of the former Russian capital by destruction of its culture and society through extermination of intellectuals. Soon the director of BDT Aleksei Dikij was arrested and imprisoned. After the most dangerous year of 1937, the family of Lavrovs managed to escape from Leningrad amidst the heat of the Stalinist repressions. The Lavrovs were at risk, because of their grandfather's Imperial past and emigration with the White Russians. In 1938 the family moved from Leningrad to Kiev, where Kirill's father, Yuri Lavrov, became a permanent member of the troupe at Kiev State Russian Drama Theatre named after Lesya Ukrainka.
During World War II Kirill Lavrov was evacuated to Kirov, then to Novosibirsk in Siberia. There he worked as a metal worker at a military-industrial plant. In the beginning of 1943, then 17-year-old Lavrov applied to join the Red Army to fight the Nazis. He was sent for training to Astrakhan at Technical School of Aviation, from which he graduated in 1945. Then he served as an aircraft technician in the Air Force, he was stationed at an Air Force Base on the Kuril island of Iturup until 1950. There he was also involved in acting with an amateur troupe at a local army club. In 1950 he was discharged from the Red Army and reunited with his parents in Kiev, Ukraine.
Kirill Lavrov did not have any theatrical training, he did not matriculate from a high school, so he was not accepted at any acting school in Moscow, when he tried to apply there. Frustrated Lavrov left Moscow for Kiev, and settled with his parents. In Kiev he became an actor of Russian Drama Theatre named after Lesya Ukrainka, where his father was among leading actors at that time. Father and son Lavrovs were involved in several stage productions together. The artistic director of Kiev Russian Drama, Konstantin Khokhlov became Lavrov's mentor, and soon invited Lavrov to move from Kiev to Leningrad, where Khokhlov was appointed artistic director of BDT. In 1955, upon Khokhlov's invitation, Kirill Lavrov moved to Leningrad and joined the troupe of BDT.