With Cahill's high-profile signing announced on Thursday by City and Football Federation Australia, Rose's exit from the Mariners - who sacked coach Tony Walmsley earlier this week - has received little fan fare.
Rose, 34, has agreed a one-year deal with City and will join the club immediately.
Rose played 165 games for the Mariners since joining them in 2010 and his Gosford exit will open the door for 22 year-old Michael Neill to claim a regular starting spot.
The World Game understands Rose won't be the only defensive addition to Melbourne City's squad with the imminent arrival of a South American defender.
