He was born in 1968 in Gdańsk to father Bogusław Michalczewski, a radio technician working for the Polish State Railways and mother Maria, an accountant.

Becoming a citizen of the now united Germany in 1991 and turning professional the same year, he was soon signed by Universum Box-Promotion, one of the leading boxing promoters in Europe.

[5] On 10 September 1994, Michalczewski, at 23-0 (18 KOs), captured the WBO light-heavyweight title with a 12-round decision over defending champion Leeonzer Barber at Sporthalle, Alsterdorf, Hamburg, Germany.

A win also would have put him just one victory short of Joe Louis' all-time record for successful defenses at any weight class.

In October 2004, it was announced that Michalczewski would come out of retirement to box France's Fabrice Tiozzo for the WBA light heavyweight title on 26 February 2005 in Hamburg.

Michalczewski was to come out of retirement to fight German boxing icon but suspected cheat Sven Ottke in Germany in May 2008, but the bout never materialized.

In 2003 Dariusz Michalczewski established foundation "Równe Szanse" (equal chances) which was aimed at supporting initiatives for youth from dysfunctional families.