Penny, 23, spent time on loan at the Vikings in 2009 while at Warrington, helping them to win the Northern Rail Cup.
Widnes Director of Rugby Paul Cullen said: “Not only does Kevin bring class, speed and proven try-scoring ability to the club, he also brings a tremendous amount of enthusiasm and positivity. The squad is feeling the bumps and bruises of a tough season so far and the addition of a player of Kevin Penny’s quality will give us the lift we need.
“It also gives Kevin the opportunity to show Denis Betts the attributes of a Super League quality winger.”
Penny, who joined the Wildcats from Warrington at the end of last season, burst on to the scene with the Wolves in 2007, scoring 15 tries in 15 games to earn himself a place in the Super League Dream Team.
He scored 11 tries in 11 games during his previous loan spell at Widnes, and also spent time on loan at Harlequins last season.
A Wakefield club statement said: “(Penny) has joined the club to allow him to play regular first team football, something that was becoming difficult to do at the Wildcats due to a surplus of impressive players in the same position.
“The Club would like to wish Kevin every success during his spell at Widnes and we look forward to seeing him back in the red, white and blue.”