The son of Max († 1980) and Franziska († 1998) Aicher, he was born in Vienna. He attended grammar school and graduated there in 1951 school respectively. In 1954, he joined the Benedictine Monastery of St. Lambrecht in Styria. He subsequently studied in Salzburg and Pontifical Athenaeum Sant'Anselmo in Rome.
He was ordinaed in 1959 and was initially chaplain in St. Lambrecht and religion teacher in the local vocational school in Murau. In 1964, he abbot Koadjutor and of 24 February 1977 until 16 January 1982, he was Abbot of the monastery of St. Lambrecht. From 1978 to 1981 he was also Abbot President of the Austrian Benedictine Congregation.
In May 1981, he was informed that he was nominated as Bishop of Linz. Aichen rejected this office several times and only gave its approval in December. On 15 December 1981 the Pope appointed him official successor of Franz Zauner. Cardinal Franz König gave him the episcopal consecration in the Conception Cathedral in Linz on 17 January 1982.
His motto was: "In Caritat serve" (in German: In love serve). He was considered a "social Bishop of Austria." Within the Episcopal Conference, he was responsible for social and political issues. The working world or the sunday rest were particular concerns for him. Under his leadership in 1990, the bishops drafted a Social pastoral letter of the Catholic bishops of Austria. Also he was involved in drafting a document on the social word of the Ecumenical Council of Churches in Austria, which was published in 2003.
In the first ten years after his inauguration, he visited all 485 official parishes of the diocese as a bishop. In 2005, he surprisingly announced his resignation for reasons of age, which on 18 may Pope Benedict XVI accepted. Thereafter, he remained at the request of the Pope for the inauguration of his successor Ludwig Schwarz.
- Churches and chapels in the parishes of the Diocese of Linz. An artistic, historical and pastoral documentation. Bischöfl. Ordinariate, Linz 2001, ISBN 3-902195-00-2
- 2005 Great Golden Medal of Upper Austria
- 2008 Erwin-Wenzl Award: Honorary Award for Lifetime Achievement
- Christine Haiden:Maximilianstraße Aichen. Bishop with the people. Trauner, Linz 2005, ISBN 3-85487-847-8
- Peter Hofer:Attentive solidarity. Festschrift for Bishop Maximilian Aichen the seventieth birthday. Pustet, Regensburg 2002, ISBN 3-7917-1846-0
- Social pastoral letter of the Catholic bishops of Austria. Osterr. Bishops' Conference, 15 May 1990 text online: 
- Aichen bishop receives the Great Gold Medal of Upper Austria = Read & article_id = 26900
- Bishop Aichen with Wenzl-prize. Oberösterreichische messages, 28 October 2008, p. 5