The 22-year-old has signed a three-and-a-half-year contract at Goldsands Stadium, where he featured 42 times on loan for the Cherries in the 2010-11 League One season.
Since then, he has had spells on loan at Leeds United, Millwall and Derby County, while making just one Premier League appearance for Spurs.
"It's great to be back," Smith told the club website. "My loan spell here a few years ago was successful and I've worked with [manager] Eddie Howe before, so it just feels right.
"This is what I need because hopefully I will get some games to improve myself and help the club move up the table.
"For a few weeks now, I've been hearing that things might be happening, but I'm happy to have it all finalised and I just want to get started."
Smith has also made six appearances for the England Under-21s. He will wear the number 15 shirt for the Cherries but isn't expected to feature in tonight's game against Huddersfield Town.