The stunning actress posed next to the Bond-branded rail vehicle at King's Cross Station's Platform 007, which was renamed for the event.
The train, which features a giant image of Daniel Craig in action as the superspy, made its maiden voyage from King's Cross to Waverly station in Edinburgh, Scotland.
Harris, who played Bond girl Eve Moneypenny in the latest movie, sipped on Skyfall Martini cocktails as one of the first passengers to make the four-hour trip.
She says, "I much prefer trains to flying."
The Skyfall train will be put into regular service from Monday (18Feb13) to coincide with the blockbuster's Dvd launch.