Bad Mitterndorf and the "Hinterbergtal", as the plateau between Bad Aussee and the Ennstal is often called, have a varied history between them.

Finds from the Tauplitzer "Lieglloch", a cave above the town centre, prove that the region was once used as a hunting area. In the Bronze Age the high valley was on the important travel route between Hallstatt and Ennstal that was regularly used. Tourists first visited Bad Mitterndorf in Roman times. The Romans knew about the thermal spring Heilbrunn and enjoyed its soothing water. Mitterndorf was first mentioned in documents in 1147. After that colonial settlements from north and south, as well as changing ownership and power relations, had a lasting effect on the region. In 1868 with the construction of the Heilbrunner Badhaus, the starting signal was given for the development of Bad Mitterndorf as a growing tourist region. In 1937, the first ski lift started operating in Tauplitz. In 1961 the Alpine Road was built on the Tauplitzalm and in 1962 the alpine pasture was opened up as a sustainable holiday region. Since 1972 Mitterndorf has been recognised as a spa town and is able to use the word Bad (spa) before its name. Since then the region has been further developed in accordance with the requirements of nature-friendly, gentle tourism, as evidenced by the most recent examples of the Mitterstein cable car or the Grimming Spa.

• around 30,000 BC Use of the Liegl cave in Tauplitz as a hunting station (bone and blade finds)
• about 1,500 BC Stations on the road Hallstatt - Ennstal (finds in Neuhofen and Kainisch)
• about 310 AD Use of the thermal spring Heilbrunn by the Romans (finds at the spring)
• 1147 first documented mention of Bad Mitterndorf
• 1335 Construction of the Catholic Church - it was dedicated to Saint Margaret of Antioch, indicating a prehistoric Roman settlement
• 1420 Transfer of the parish Pürgg and the Vicariate Mitterndorf to the Wiener Neustadt monastery by Archduke Ernst
• 1491 Award of the St. George Order of the Knights to Mitterndorf and its parent parish Pürgg
• 1577 Transfer of the district its control to the Graz Jesuit College
• 1577-1730 the valley was under the spiritual and secular sovereignty of the Jesuits
• 1591 Construction of the Castle Grubegg, which in 1606 was taken from the control of Hinterberg
• 1597 Beginning of two years of riots when a Protestant pastor (appointed 1595) was replaced by a Catholic priest
• 1610 The transition of secular rule to the Jesuits
• 1680 Founding of the elementary school Mitterndorf
• 1714 Outbreak of the plague in Mitterndorf
• 1717 Construction of the Stations of the Cross and the statue of Mary on Kumitzberg by Balthasar Marinz, start of pilgrimages to Maria Kumitz
• 1741 Construction of a powder mill at the bottom of the Grubegg estate
• 1773 Construction of the church Maria Kumitz
• 1796 Commissioning of a tug mill and track hammer for the production of sheet metal by the Hallamt (Salzamt)
• 1808 Post office built
• 1868 Opening of the first bath-house in Heilbrunn and construction of the Salzkammergut railway 
• 1961 Construction of the alpine road on the Tauplitzalm
• 1962 Construction of the first hotels and guesthouses, development of the thermal spring Heilbrunn
• 1972 Mitterndorf recognised as a spa resort,  may now use the name "Bad Mitterndorf"  (Bad = Spa)
• 1980 Bad Mitterndorf recognised as a market town
• 2009 Opening of the Grimming Spa
• 2010 Opening of the Mitterstein cable car to Tauplitzalm
• 2015 Merger of the municipalities Bad Mitterndorf, Pichl-Kainisch and Tauplitz to the larger municipality of Bad Mitterndorf