The 26-year-old Wales international full back has joined Orient on an initial one month loan deal.
"I'm keen to get some minutes under my belt and hopefully help the lads up the table," he told the official Leyton Orient website.
"I've not played a huge amount as it's tough to get into the side at Birmingham at the minute.
"I'm fit and raring to go and I jumped at the chance to come here when I heard of the interest."