The earliest signs of human life in Mikkeli are the Astuvansalmi rock paintings in Ristiina, dating back to 4000-2200 BCE.
The Astuvansalmi is the largest rock painting site in the Nordic countries.

The peace treaty of Nöteborg in 1323, with which the Pogosta (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.
The locality received its present name Mikkeli after Archangel Michael by the early 16th century at the latest.

On 23 January 1597 more than 200 peasant rebels were killed in the parsonage of Kenkävero in part of the larger Cudgel War.

In the war waged by King Gustav III of Sweden against Russia 1788–1790, a battle took place at Porrassalmi Strait, a few miles south of Mikkeli, on 13 June 1789.
In the battle the Swedes (the Finns) victoriously defended their positions against superior numbers of Russians.

Mikkeli was granted town rights in 1838.
 The provincial government of the province of Mikkeli that had been established in 1831, moved from Heinola to Mikkeli in 1843.

In 1918 during the Civil War, the headquarters of the White Army were established in Mikkeli.
 Mikkeli was located in a conservative farming area and it was a White stronghold.
But elements of the Russian army garrison in the area supported the Reds.
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.

During the Winter War and Continuation War, the headquarters of the Finnish Army was located in Mikkeli.
The Army staff made their base in a local secondary school.
At the site of that school is the small Headquarters Museum (Päämajamuseo) containing photographs and memorabilia of the era.
 Because the headquarters of the army was based there, Mikkeli was bombed heavily.
But since there was almost no "high-rise" development at that time, the damage was quickly repaired.
Architecturally most of prewar Mikkeli doesn't exist anymore.

Wartime Mikkeli is identified with Marshal Mannerheim, the commander of the Finnish army 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.
It is possible to look inside the carriage through its windows at any time.
But public entry to the carriage is only permitted once a year, on Mannerheim's birthday (4 June).
The carriage was the venue of Mannerheim's famous 1942 meeting (near Immola) with Hitler, on which occasion a private conversation between the two men was secretly recorded.
Photographs of this meeting are on display in the carriage.
Mannerheim was a regular diner at the Mikkelin Klubi, where his favourite drink was schnapps.

One of the main museums in the town is the Infantry Museum (Jalkaväkimuseo) located in one of the former army barracks, close to the University of Applied Sciences.
It contains exhibits from the four wars in Finland's modern history – the Civil, Winter, Continuation and Lapland Wars.
The museum also contains an exhibit dedicated to Finnish war hero Lauri Törni.

In 1986, there was a hostage crisis in Mikkeli, when a bank robber drove from Helsinki to Mikkeli with three hostages and parked there.
When the police shot at the hostage taker's car, he exploded the car, killing himself and one hostage.

In 1997 there was a province reform, which made Mikkeli the capital of the new province of Eastern Finland.
In a separate reform, the rural municipality of Mikkeli which had surrounded the town and the municipality of Anttola were consolidated to Mikkeli in the beginning of the year 2001.
The municipality of Haukivuori was consolidated with Mikkeli on 1 January 2007 and Ristiina and Suomenniemi in 2013.
The earliest signs of human life in Mikkeli are the Astuvansalmi rock paintings in Ristiina, dating back to 4000-2200 BCE. The Astuvansalmi is the largest rock painting site in the Nordic countries.
The peace treaty of Nöteborg in 1323, with which the Pogosta (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. The locality received its present name Mikkeli after Archangel Michael by the early 16th century at the latest.
On 23 January 1597 more than 200 peasant rebels were killed in the parsonage of Kenkävero in part of the larger Cudgel War.
In the war waged by King Gustav III of Sweden against Russia 1788–1790, a battle took place at Porrassalmi Strait, a few miles south of Mikkeli, on 13 June 1789. In the battle the Swedes (the Finns) victoriously defended their positions against superior numbers of Russians.
Mikkeli was granted town rights in 1838.  The provincial government of the province of Mikkeli that had been established in 1831, moved from Heinola to Mikkeli in 1843.
In 1918 during the Civil War, the headquarters of the White Army were established in Mikkeli.  Mikkeli was located in a conservative farming area and it was a White stronghold. But elements of the Russian army garrison in the area supported the Reds. 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.
During the Winter War and Continuation War, the headquarters of the Finnish Army was located in Mikkeli. The Army staff made their base in a local secondary school. At the site of that school is the small Headquarters Museum (Päämajamuseo) containing photographs and memorabilia of the era.  Because the headquarters of the army was based there, Mikkeli was bombed heavily. But since there was almost no "high-rise" development at that time, the damage was quickly repaired. Architecturally most of prewar Mikkeli doesn't exist anymore.
Wartime Mikkeli is identified with Marshal Mannerheim, the commander of the Finnish army 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. It is possible to look inside the carriage through its windows at any time. But public entry to the carriage is only permitted once a year, on Mannerheim's birthday (4 June). The carriage was the venue of Mannerheim's famous 1942 meeting (near Immola) with Hitler, on which occasion a private conversation between the two men was secretly recorded. Photographs of this meeting are on display in the carriage. Mannerheim was a regular diner at the Mikkelin Klubi, where his favourite drink was schnapps.
One of the main museums in the town is the Infantry Museum (Jalkaväkimuseo) located in one of the former army barracks, close to the University of Applied Sciences. It contains exhibits from the four wars in Finland's modern history – the Civil, Winter, Continuation and Lapland Wars. The museum also contains an exhibit dedicated to Finnish war hero Lauri Törni.
In 1986, there was a hostage crisis in Mikkeli, when a bank robber drove from Helsinki to Mikkeli with three hostages and parked there. When the police shot at the hostage taker's car, he exploded the car, killing himself and one hostage.
In 1997 there was a province reform, which made Mikkeli the capital of the new province of Eastern Finland. In a separate reform, the rural municipality of Mikkeli which had surrounded the town and the municipality of Anttola were consolidated to Mikkeli in the beginning of the year 2001. The municipality of Haukivuori was consolidated with Mikkeli on 1 January 2007 and Ristiina and Suomenniemi in 2013.
Mikkeli