In a statement announcing the achievement, McCain said he was "both honored and humbled" to have amassed such a following. "It has been one of the most enjoyable experiences in my long political career – not too bad for an old guy," McCain added.
McCain's increasing use of Twitter marks a major shift from the presidential campaign when he said he "never felt the particular need to e-mail."
Earlier this year, McCain also became the proud owner of new BlackBerry.
In addition to slightly more than a million followers on Twitter, McCain boasts more than half a million supporters on Facebook.