Mieczysław Kamieński, coat-of-arms Ślepowron, was born on 22 February 1833 in Lviv to Mikołaj Kamieński and Adamina, née Potocka. He spent his childhood and youth in France, where, thanks to the Montebello family's patronage, he attended the military school in La Flèche for four years. He dreamt of further military education at the prestigious school in Saint-Cyr, but was not accepted due to his non-French background. After leaving school, he undertook service as a major in the navy and made sea voyages, reaching Bolivia, Chile and Mexico, among other places. After this period of his life, he studied mineralogy for a year in the famous caves near Freiberg in Saxony.

In 1859, following the outbreak of the Italo-Austrian War, Kamienski volunteered for the Foreign Legion. He began fighting as a private grenadier. At the Battle of Magenta, which took place on 4 June 1859, he was severely wounded in the right shoulder. Transported to hospital in Milan, he struggled in pain for three months and died in his father's arms on 2 September 1859.

For his bravery at Magenta, he was promoted to the rank of corporal and awarded the medal for the Italian campaign. He was also awarded the Cross of the Legion of Honour at the request of General Montebello.

Kamienski left behind poems and fragments of prose. These manuscripts are kept in the Polish Library in Paris. His death was widely echoed in émigré circles and the European press - it was reported in the Milan Gazette, the Poznan Journal and the French Journal des Débats. Cyprian Kamil Norwid, in a letter to Seweryn Gałęzowski in October 1859, stated that Kamieński's will should be publicly read in schools as a model of Christian and civic virtues.

In accordance with his last will, he was buried in the Montmartre cemetery in Paris, alongside other Polish émigrés. The solemn funeral, which took place on 30 December 1859 after a service at the Ste-Marie-Madeleine church, brought together many Poles, French and Italians. Speakers at the grave included Jan Ledóchowski and Giannone, an Italian from Modena. Kamieński's father, deeply moved by the loss of his only son, commemorated him with a book Mieczysław Kamieński, tué à Magenta, published in 1861 in Paris, and with notes entitled A short life, a long sorrow and a three-month-long dying of an only son.