He said he had no choice but to seek welfare because he could not feed a family on what he earned as a first class cricketer, paid for only six months of the year.
"The reality is this is what it's like," Sinclair said. "It has been quite a tough decision to make.
"It has been very hard to look for some sort of meaningful employment."
Australian-born Sinclair, who played 33 tests and 54 one-day internationals, made 214 on test debut against the West Indies in 1999; then the second-highest total by a debuting batsman.
Though he made 204 against Pakistan the following season and was a prolific scorer in first class cricket - with more than 13,000 runs - Sinclair struggled to command a regular place in New Zealand's team.
He was dropped from the New Zealand contract list in 2007, though he was recalled for one test against Australia in 2010.