Shaheen tweeted that the photo, a horizon view from Hampton, N.H., was taken by a constituent named Chip Moynihan.
GOP Whip Kevin McCarthy (Calif.) opted into the new design later in the day.
Twitter announced the new design function on NBC's "Today" show, so the Twitter blog points to examples of newly designed profiles at "Today" anchors' accounts like @MLauer, @SavannahGuthrie, @AlRoker, and this morning's guest anchor @RyanSeacrest.
The new option is available under design settings on individual Twitter accounts.
Updated at 3:29 p.m.