EurosportSteven, who had 15 disposals in Saturday night's 71-point AFL loss to Essendon at Etihad Stadium, was given a random breath test by police on his way to a recovery session at the club's Seaford base on Sunday morning.
The 22-year-old returned a reading of 0.08 and was fined $423 and his driving licence was suspended for six months, the Saints said in a statement.
St Kilda have also fined Steven $5000.
"While Jack believed he would be alright to drive on the morning following the club's match against Essendon, he has made an error of judgement that is clearly unacceptable by the community and the standards expected at the St Kilda Football Club," St Kilda's head of football Chris Pelchen said.
"Jack has apologised for his mistake and acknowledges the broader responsibility that comes with being an AFL footballer."
The AFL and the players' association have agreed with the sanctions imposed, the Saints added.
St Kilda play Brisbane at the Gabba on Saturday night.
In better news for the Saints, defender Jarryn Geary on Monday extended his contract with St Kilda until the end of the 2014 season.
The 24-year-old Bendigo Pioneers product has played 64 games including 12 this year.
Ben McEvoy, Sam Fisher, James Gwilt and Rhys Stanley have also re-signed with the Saints in recent weeks.
"It's a fun place to be around and it's great to have players like Lenny Hayes, Stephen Milne and Nick Riewoldt to learn from. They're just champions of the game," Geary said.
St Kilda coach Scott Watters said the 183cm Geary had stamped himself as a capable small defender.
"Jarryn has taken significant steps forward this year and has become a consistent contributor, marking some of the most dangerous small forwards in the game," Watters said.
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