Campbell has made a big impact at Hull City since joining the Tigers in October, scoring six times in 12 starts.
Hull manager Phil Brown had been desperate to retain Campbell's services, said earlier in the week: "Anybody who scores goals is an important asset.
"His sort of goal strike-rate would be appreciated in any division. As far as I'm concerned, it is a no-brainer - I'd like to keep him until the end of the season."
Shawcross will stay at Championship promotion contenders Stoke after making 24 appearances since arriving at the Potters in August.
And Martin, who joined Plymouth in October, has been in good form at Home Park, scoring twice in eight starts.