Harold Holcroft (12 February 1882 – 15 February 1973) was an English railway and mechanical engineer who worked for the Great Western Railway (GWR), the South Eastern and Chatham Railway (SECR) and the Southern Railway (SR).
At the GWR, Holcroft helped the Chief Mechanical Engineer (CME), George Jackson Churchward, design the 4300 class 2-6-0 Moguls, and took the design principles for this class of locomotive with him when he moved to the SECR. Here, he worked as Assistant to Richard Maunsell and was involved with the design of the Maunsell Moguls, transferring to the Southern Railway when it was created by the amalgamation of the SECR with other railways at Grouping in 1923. After Maunsell's retirement in 1937, Holcroft continued to work for the Southern Railway under Oliver Bulleid until his retirement in 1946.