The US-listed group is offering $5.25 per share for the 86.5% stake in GFI it does not already control.
BGC said it had notified the GFI board of directors by letter on Tuesday regarding the launch of its tender offer.
The fully-financed tender offer will expire at midnight on 19 November 2014, unless BGC opts to extend it.
BGC said its offer represents a 15% premium to the $4.55
