Melbourne’s injury crisis prompted the club to make a move for the player, who debuted for his country in the 2013 Rugby League World Cup.
Fiji made a big impression at that tournament, and Koroibete played in all five games of his country’s campaign.
He has scored 12 tries in 16 games for Wests, and is known for his electrifying pace as well as being an natural try scorer.
Melbourne Storm Football Director Frank Ponissi said: “An opportunity came up to bolster our depth to our outside backs and with limited chances at the Tigers this season, we saw Marika as an exciting talent who was coming off contract at the end of the season.
“Marika has displayed outstanding form in the NSW Cup, he is the leading try scorer of the competition with 15 and we see his signing as adding strength to our roster.”
The player is expected to be placed into the Storm squad immediately.