The 32-year-old returns to England after three seasons in Scotland with St Johnstone, Queen of the South and St Mirren, who won the Scottish League Cup last season.
Parkin said: "Exeter were looking to bring in a front player and fortunately after having a meeting with the manager and a really good chat, I've been down to have a look at the place and I'm really delighted to have signed.
"I know that Exeter have got a tradition of playing good football and the manager has obviously got a great reputation, so it was a no-brainer really.
"I'm just delighted to get another opportunity down here to play football and hopefully be part of a successful team."
Parkin started out at Chelsea, had a prolific spell at Swindon and went on to play for Ipswich, Luton and Walsall before heading north of the border.