Diaconu was born in Ploieşti, Romania, but fought out of Montreal, Quebec, Canada for almost his entire professional career.

"[2] On 19 April 2008, Diaconu won the vacant WBC interim title with a twelve-round unanimous decision over Chris Henry in Romania; the interim title being at stake to allow full titleholder Chad Dawson to make an optional defense after a previous injury-produced delay to the mandated bout.

In July 2008, Diaconu was elevated to full champion status after Dawson vacated the title to avoid having to make the mandatory defense.

[3] Diaconu suffered his first career defeat and lost the WBC world title to Jean Pascal on 19 June 2009, and would go on to lose a rematch on 11 December 2009.

A year later, Diaconu announced his retirement from boxing, stating that he felt a lack of support from his promoters, Interbox, to organize significant fights for him.