The actress played the role of super spy Sydney Bristow in the 2001 show.
"I wrote Alias thinking about her," Abrams said Friday during a conversation with Chris Rock at the Tribeca Film Festival in downtown Manhattan, as part of the fest's ongoing Director Series.
"I finished it, she came in, was amazing. And I remember someone at the network was like, 'I don't know, is she hot enough?' "
Garner went on to snag the role, playing the stealth double agent for five seasons until 2006.
"Jen was so great, and she did everything. And it was incredible doing the pilot, I remember watching her kind of find this strength in herself. It was just so cool to see, and she just did a spectacular job," he said of the 43-year-old actress.