Ex-Warrington forward Pickersgill, 27, is in his fifth season with the Vikings, while Joseph, 28, joined them at the start of this year from Bradford on a one-year deal.
Widnes coach Denis Betts said: "These signings show the stability we are trying to add within our squad."
He added: "Steve Pickersgill has proved his worth to the team on a number of occasions and for a while he's just been on one-year deals.
"I believe the timing is now right to give him some stability and help him to advance his career further.
"Exactly the same applies with Phil Joseph. I've also been really pleased with his contributions in the relatively short time he has been with us."