Paul Sheerin was appointed the Bairns head coach at the end of May after the club failed to get out of League One, and he has made key additions to his backroom team.
The 34-year-old has recently been manager at English non-league side Workington.
“I’m looking forward to, hopefully, pushing the club forward,” Grainger, who also counts Gretna, St Johnstone and Dundee United as former clubs, told the Falkirk website.
"As soon as I spoke to Paul I knew it was the right move for me and I can’t wait for the challenges ahead and to work alongside him.”
Caig played for Hibs between 2001 and 2003 during a career which spanned 27 years.
The 47-year-old is an experienced goalkeeping coach – the role he will have at Falkirk – having had spells at Hartlepool United, Bury FC and Livingston.
“I’m delighted to be here,” he said.
“I worked with Gary Holt at Livingston when he was manager there. I’m delighted to be here and hopefully I can be of help along the way this season.
“It’s something fresh, something new. Pre-season’s not far away, so we’ll be getting to work with the players, the new Head Coach and hopefully we can get off to a good start and have a good season.”