The controversial move comes almost four years after McCormick caused the deaths of brothers Arron and Ben Peak, aged 10 and eight respectively, while driving with excess alcohol in a crash on the M6 in Staffordshire.
The former Pilgrims stopper was sentenced to seven years and four months in prison in October 2008 after he admitted to the charge, but is set to be released after serving half of the original figure.
McCormick has already been put through his paces having trained with Swindon since January while on day release. He will join Paolo Di Canio's squad on their pre-season tour of Italy.
Swindon chairman Jeremy Wray told BBC Wiltshire: "Our sympathy is with the family of the victims - that will never change. There's been a complete tragedy and lives have been destroyed.
"This guy has done his time in prison. He wants to come back and give something back to society. The best way we can do that is to rehabilitate, and that's the role Swindon can play. It's a benefit we've thought about in the long-term. It's going to be a big debate and I'm not frightened of it."