Lieutenant Lewis was a security officer assigned aboard the USS Enterprise, under Captain James T. Kirk.
On stardate 3196 he was part of Lieutenant Commander Giotto's team on Janus VI, hunting for the mother Horta. When Giotto broke his team down, he assigned Lewis and Vinci as two of the team leaders. (TOS: "The Devil in the Dark")
In 2267, he and Captain Kirk exited the turbolift onto the bridge of the Enterprise as the search for a cordrazine-injected Leonard McCoy progressed aboard the ship. (TOS: "The City on the Edge of Forever")
In 2268, he was among the honor guard that stood at attention upon the arrival of Vulcan Ambassador Sarek. (TOS: "Journey to Babel")
The same year, Lewis kept his phaser trained on Jojo Krako when the latter beamed aboard the Enterprise. (TOS: "A Piece of the Action")
In 2266, Lewis was present on the wedding of Robert Tomlinson and Angela Martine, which was interrupted by Romulan sightings near the Neutral Zone. (TOS: "Balance of Terror")