Shamrock was designed by third-generation Scottish boatbuilder, William Fife III, Jr., and built in 1898 by J. Thorneycroft & Co., at Church Wharf, Chiswick, for owner Sir Thomas Lipton of the Royal Ulster Yacht Club (and also of Lipton Tea fame). However her draft was too great for construction at Chiswick and she was built at Millwall.
Shamrock was built of all-metal construction, with a steel frame and a pine deck. She was skippered by Captain Archibald "Archie" Hogarth.
Shamrock (also known as Shamrock I, to distinguish it from its successors) was built in 1898 under a shroud of secrecy, and christened by Lady Russell of Killowen at its launch on June 24, 1899.
During its trials it raced against the 1895 America's Cup challenger, Valkyrie III, as well as twice beating His Majesty's Yacht Britannia in regattas on the Solent. It sailed to New York for the America's Cup race in the summer of 1899. The Cup defender Columbia beat Shamrock in all three races. It returned to Britain in the autumn of 1899, towed by Lipton's steam yacht, Erin. It was subsequently refitted by Lipton and used as a "trial horse" to test the later challengers, Shamrock II, III, and IV.