At the age of 30, he started investing in Belgian steel factories and by the end of the 1970s he practically controlled the whole steel industry in the region of Charleroi. He foresaw the coming steel crisis of the late 1970s and sold his enterprises to the Belgian state after merging them with the competing steel firm Cockerill to create Cockerill-Sambre.

Frère used the proceeds from this sale to build an investment empire around the Swiss holding company Pargesa which he founded with the Canadian investor Paul Desmarais. Pargesa took over the Belgian holding company Groupe Bruxelles Lambert in 1982 and over the year added significant stakes in such wide ranging Belgian companies as Petrofina, Royale Belge Insurance, Compagnie Luxembourgoise de Télédiffusion (CLT), and Tractebel. He actively promoted international consolidation of the sectors in which he was involved, selling Banque Bruxelles Lambert to ING Group, Royale Belge to AXA, Tractebel to Suez, Petrofina to Total S.A., and RTL to Bertelsmann.

Frère is married and has three children. His first wife was Nelly Poplimont, and they had a son, Gérald. His second wife is Christine Henning, and they have had two children, Ségolène, and Charles-Albert, who died in 1999, in a car accident at the age of 19.

In 2002, he received the title of baron from the Belgian king Albert II. He is a co-owner, together with Bernard Arnault of LVMH, of the Château Cheval Blanc winery near Bordeaux. He is a member of the Cercle Gaulois.

2014 : Knight Grand Cross in the Legion of Honour.