The 26-year-old has agreed the switch to Roots Hall after being released by Colchester United at the end of last season.
He is Phil Brown's first signing as Southend manager.
"John is exactly the type of player we're looking for here at the club for the new season," Brown told Southend's official website.
"He's a really solid defender who can play anywhere across the back four, but predominantly as a right-back.
"It's good to have him in early because now he's got five weeks with the lads to get to know them and be ready for the new season."
White's move to Southend will be officially completed on July 1.