The 30-year-old played an integral role in his side's triumph in Brazil as they defeated Argentina in the final to claim his country's fourth world title.
He told the Daily Mail: "I knew it. It was clear to me before the tournament it would be my last one. It wasn't because we won the World Cup that I retired. I'd made my mind up before the tournament.
"I invested all my energy and capabilities in the World Cup as it was my last time and I didn't want to end up in a position where I might think I hadn't tried everything. That's how I approached the tournament."
Lahm made 113 appearances for Germany during his 10-year international career.