He was awarded the title of professor in 1907 and was promoted to honorary doctor of medicine in 1919.

[3] Heikel helped found and taught at the Nya svenska samskolan, a private co-educational school in Helsinki, in 1888.

He was opposed to modern sports with its specialization, competitiveness and pursuit of records, while Artur Eklund, in a polemic with Heikel, expressed himself pejoratively about gymnastics.

In the 1860s, together with his sister Anna Heikel, he helped introduce the Baptist church to Finland.

[8][11] Critical of the Evangelical Lutheran Church of Finland, he supported the foundation of the Association for Religious Freedom and Tolerance in Finland (Swedish: Föreningen för religionsfrihet och tolerans i Finland, Finnish: Suomen uskonvapaus ja suvaitsevaisuusyhdistys) in 1887;[3] he was also involved in the Prometheus student society which campaigned for freedom of religion.