[6] The earliest signs of human life in Mikkeli are the Astuvansalmi rock paintings in Ristiina, dating back to 4100-2000 BCE.

[8] The peace treaty of Nöteborg in 1323, with which the pogost (church parish) of Savilahti was transferred from the control of Novgorod to Sweden, is the oldest written record of the settlement in the present region of Mikkeli.

In the war waged by King Gustav III of Sweden against Russia, the Battle of Porrassalmi took place a few miles south of Mikkeli on June 13, 1789.

A major engagement was fought around the railway station at Mäntyharju, about 20 km (12 mi) to the south of Mikkeli, when the Whites blocked a Red thrust coming north out of Kouvola.

At the site of that school is the small Päämajamuseo (Finnish for 'Headquarters Museum') containing photographs and memorabilia of the era.

As a result of serving as the headquarters of the army that was based there, Mikkeli was bombed heavily, but since there was almost no high-rise development at the time the damage was quickly repaired.

Wartime Mikkeli is identified with Marshal C. G. E. Mannerheim, the supreme commander of the Finnish Defence Forces and later President of Finland.

His personal railway carriage, which he used as a command post during the war, is parked in a siding at Mikkeli Station.

In 2024, there were plans to establish a sub-staff of ground forces working under the military alliance in Mikkeli following Finland's admission into NATO.

Mikkeli has a subarctic climate (Dfc), bordering on humid continental (Dfb), as May and September average just slightly below 10˚C (50˚F).

[21] As English and Swedish are compulsory school subjects, functional bilingualism or trilingualism acquired through language studies is not uncommon.

The most common foreign languages are Russian (1.4%), Ukrainian (0.5%), Arabic (0.4%) and Estonian (0.3%)[21] As of 2023[update], there were 2,855 persons with a migrant background living in Mikkeli, or 5.5% of the population.

[24] A central campus of South-Eastern Finland University of Applied Sciences (Xamk) is located in Mikkeli and is a major employer in the city.

Its history dates back to 1965, when Mikkeli was selected as the site for a new higher education college specializing in professional, engineering and vocational studies, enrolling its first class of students in 1969 while situated in an old Russian Army barracks on the outskirts of town.

[25] Aalto offers a highly ranked Bachelor of Science degree in international business, taught in English, which draws students and faculty from around the world.

The concert hall is the home of St. Michel Strings chamber orchestra, and also provides the main venue for the annual Mikkeli Music Festival, which attracts musicians and audiences from across Europe.

A well-known and popular travel centre and theme park Visulahti is in Mikkeli, located in the shores of Lake Saimaa.

Due to Mikkeli's role as the headquarter city in World War II, the town has several museums dedicated to that period of time.

Jukurit is an ice hockey team from Mikkeli, which competes in the Finnish premier league, Liiga.