Whitelegg began his career as an engineering pupil with Sharp, Stewart and Co., afterwhich he worked for Neilson Reid & Co, in Glasgow and then Hamilton Windsor Ironworks Co. who were based in Garston, Liverpool. After working on engineering design for locomotives for GER, whilst at Ruston Proctor & Co., he was given employment at the GER drawing office at the Stratford works. He remained there until 1879, when he was appointed Locomotive Carriage & Wagon and Marine Superintendent, LTSR, at Plaistow Works. He was the first LTSR locomotive superintendent. He retired in 1910.