Reports in the Portuguese press earlier on Tuesday suggested Marseille had agreed to Lucho's demands and offered the 28-year-old a highly lucrative deal.
The two clubs had been locked in talks since Friday but a compromise about the fee involved in the deal was only reached today.
Porto have agreed to sell Lucho to Marseille for €18 million, a fee that could rise to as much as €24 million depending upon the player's performances for his new club.
"An agreement has been reached in principle between both parties," Marseille declared on their official club web site.
The Argentina international is now expected in Marseille in the coming days to undergo a medical and sign a four-year contract with the French giants.
Lucho, who joined Porto from River Plate in 2005 for a fee in the region of €10 million, had been an integral piece of the Dragons since his arrival.
The Portuguese champions are now in the market for a new player, with reports indicating that Newcastle's Jonás Gutiérrez has been identified as a possible replacement for the now Marseille-bound ace.
Luís Mira, Goal.com