Halifax 20-26 Rovers FT
Bulldogs 26-28 Eagles FT
Raiders 60-0 Thunder FT
Whitehaven 21-20 Knights FT
Hunslet 32-12 Skolars FT
The 22-year-old Australian threequarter, who has scored 16 tries in 19 appearances since joining the Vikings from St George Illawarra last August, was out of contract this year and thought to be attracting attention from Super League rivals.
Now Runciman has signed a two-year extension which, subject to him meeting visa requirements, will keep him at the club until the end of 2018.
Widnes coach Denis Betts said: "I am extremely pleased that Charly has decided to commit to us for the next two years. He has been a fantastic acquisition since he arrived at the end of last year.
"He helped us retain our place in Super League with his fantastic performances in the Super 8 Qualifiers.
"Charly took a chance and came over here and he has added massively to everything we do."
Runciman said: "I have enjoyed my time here and I am excited about what is to come in the future.
"To be part of a club that is proving it is moving forward is really exciting for me and my team-mates."