His mother, Lyudmila Ippolitovna was from a small village in Western Ukraine, she graduated after seven classes and spent her whole life working as a dispatcher at a bus station.

Sergei's father, Leonid Trofimovich Garmash was a driver at first, then graduated from the institute and began to work in leadership positions.

Garmash's significant roles include Major Korotkov in the detective series Kamenskaya, where he acted for five seasons, Yevgeny Markerants in the Mechanical Suite (2001) by Dmitry Meskhiev, Ivan in "Lover" (2002) by Valery Todorovsky, senior warrant officer Nikolai Krauz in the film 72 Meters by Vladimir Khotinenko, drunkard Yasha in Poor Relatives (2005) by Pavel Lungin, Major Popov in Katyn (2007) by Andrzej Wajda, Mels's father in the hit 1960s set musical Stilyagi (2008) by Valery Todorovsky.

Additionally, Sergei acted in the films Soundtrack of Passion (2009), Black Lightning (209), Lucky Trouble (2010), "Once" (2013), "The End of the Beautiful Era" (2015), The Duelist (2016), the series The Hethers of Major Sokolov (2014), Leningrad 46 (2015), The Investigator Tikhonov (2016) and Murka (2017), etc.

He also appeared in Going Vertical, Matilda, as well as the comedy-adventure Partner, where he played a major police officer Khromov, whose soul and mind were transferred to the body of a year-old child.