Haworth, 24, who began his career at Blackburn and has also played for Rochdale, Bury, Oxford, Bradford and Falkirk, has agreed a six-month deal at Meadow Lane.
Meanwhile, 22-year-old Labadie, who made 29 appearances and scored two two goals last season, has signed a new one-year contract.
He told the club's official website: "I'm chuffed to bits because it's been going on all summer and I can kick on now and concentrate on the season ahead.
"I want to build on last year, play more games and I want to score more goals and do as well as I can for Notts County Football Club.
"I'm 22 now and I want to be playing every game and I really want to make a name for myself this season."