Central midfielder Welsh, a former captain for the Lilywhites, was an integral part of the team that hit some late-season form and got promoted out of the League One play-offs, playing 44 times in total.
Jamaica international Humphrey turned out on 12 more occasions and the pair have followed Wembley hero Jermaine Beckford in signing up for the next two terms.
“After completing Jermaine’s deal on Monday more pieces of the jigsaw are being put in place with hard work behind the scenes,” said North End boss Simon Grayson.
“Getting John and Chris signed up is more positive news and we are delighted they have committed their futures to what we are building at Deepdale.”
Welsh, who joined in the summer of 2012, one year before Humphrey arrived, added: “I’m glad it’s sorted and I can concentrate on getting myself fit and I’m looking forward to getting back for pre-season.
“Obviously it is always in the back of your mind, it’s your livelihood and your future, but my main aim was to get promoted with this club and that’s firmly all I was focusing on.
“After that, luckily we got the ball rolling straight away and now it is done and dusted and I’m grateful for that.”
Wide-man Humphrey, 27, has played in the Scottish top flight with Motherwell and is excited about plying his trade in England’s second tier.
“I’m delighted, It has been brilliant to get the deal done and sorted and so early as well; I can go enjoy my summer and look forward to next season now,” he said.
“It’s a massive challenge for me, it’s one of the leagues I’ve always wanted to play in for a long time now.”