Boss Harry Redknapp has been eager to secure reinforcements up front since the transfer window opened due to the loss of Kanu and John Utaka to African Nations Cup duty.
Baros passed a medical at Fratton Park today and will begin training on the south coast tomorrow.
"It's a terrific opportunity to have a look at him," Redknapp told the club's website, portsmouthfc.co.uk. "It's a loan deal until the end of the season and then we'll see how it goes from there."
Baros has failed to make an impact with Lyon and has found himself out of favour out of favour at the Stade Gerland.
But Redknapp is convinced he has signed a player of real quality.
"He's got pace and he makes good runs."