Shamrock (also known as Shamrock I, to distinguish her from her 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 her trials she raced against the 1895 America's Cup challenger, Valkyrie III, as well as twice beating HMY Britannia in regattas on the Solent. She 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. She returned to Britain in the autumn of 1899, towed by Lipton's steam yacht, Erin. She was subsequently refitted by Lipton and used as a "trial horse" to test the later challengers, Shamrock II, Shamrock III, and Shamrock IV.