Magoffin, now coached by Tom Moody, formerly in charge at Worcestershire after playing for the Midlands club, took 29 wickets at a low average of 23.31 for his state during in Australia's first-class Sheffield Shield last season.
"Steve is a tall and lively 'hit the deck' bowler who has excellent control," Worcestershire director of cricket Steve Rhodes said of the 28-year-old.
"This will make him a tough opponent to face on the early season English wickets," the former Worcestershire and England wicket-keeper added.
"He is highly recommended by Tom Moody who is his coach at West Australia and we are delighted to give him an opportunity to make a name for himself in England."
Fast-medium bowler Magoffin said: "I am delighted to be joining Worcestershire CCC at the start of the season.
"My coach at Western Australia, Tom Moody, speaks very highly of the club, the squad and the setup at New Road and I can't wait to join up with Steve Rhodes, Vikram Solanki and the rest of the team.
"I am very eager to pull on the shirt for Worcestershire and get the ball in my hand for the season opener against Warwickshire".
Magoffin will join his new club in April and will stay at Worcestershire until June 9, when West Indies fast bowler Fidel Edwards arrives for the second-half of the season.
Worcestershire suffered major disruption last year when their New Road headquarters ground in Worcester spent weeks under water because of floods.
The county said Thursday they'd reached an agreement with nearby Kidderminster Victoria Cricket Club to move matches there at 48 hours notice in the event of fresh flooding.
Worcestershire added that in return they would invest a total of 50,000 pounds (100,000 dollars) into the Chester Road ground over a five-year period, with funds initially targeted at improving facilities for players and umpires.