Jack Phillips, the vessel's senior wireless operator, wrote the postcard in March 1912 to his sister, Elsie, while at port in Belfast, Ireland, where the Titanic was built. Construction was completed at the end of March, and it left the dock on April 2, 1912.
The correspondence, written on a 5.5 inch by 3.5 inch postcard, features an image of the Titanic during its construction and is postmarked in Belfast.
The card reads in part, "Very busy working late. Hope to leave on Monday & arrive So'ton (Southampton) Wednesday afternoon. Hope you quite OK."
The message ends with the words "Love, Jack."
"Phillips often chose postcards which depicted the ship on which he served," said Bobby Livingston, executive vice president of Boston-based RR Auction, which is selling the card.
"According to our research, only five of the 300 postcards retained by Elsie had any relation to Titanic, and only two featured the ship as the front photograph making this an exceptionally rare example," Livingston said in a statement.
Livingston says Phillips is a forgotten hero who saved many lives as the Titanic started sinking. Phillips worked tirelessly to send messages to other ships to enlist their help in rescuing the passengers and crew.