Mr Tantazzi is to be succeeded by Paolo Scaroni, chief executive of energy firm Eni, and will replace the outgoing post holder in a non-executive capacity with immediate effect.
Massimo Tononi has also been appointed as an independent non-executive director at the organisation, the LSEG explained.
Chris Gibson-Smith, chairman of LSEG, said: "I would like to thank Angelo for his significant role in the development of Borsa Italiana and for his contribution to the LSEG board.
"Angelo will continue to chair the board of Borsa Italiana until next year so we will benefit from his experience within the group until then. I am delighted to welcome Massimo Tononi to the board.â
In April Massimo Capuano, the then deputy chief executive officer (CEO) at LSEG, announced he would step down from his role with the organisation and from his role as deputy CEO of Borsa Italiana.
By Jim Ottewill