In his report dated 8 March 1847, civil engineer John Hawkshaw was able to report to the Lancashire & Yorkshire Railway Company that all of the line's tunnel shafts had been sunk and around 200 yards of the Cumberworth Tunnel had been excavated.
The line formally opened on 1 July 1850.
On the evening of Saturday 12 January 1861, the 9:26pm departure from Penistone derailed at around 30 mph in the tunnel, with the engine decoupling from the three carriages and guard's van. The engine came to halt after around 160 yards, tearing up track as it went. The carriages came to a halt about 30 yards behind the engine and angled across the track. Surprisingly, none of the passengers suffered any injuries, although the guard, Joseph Handley, was thrown to the floor of his van. Whilst Handley ran to Denby Dale Station, the fireman went back to Penistone where a "telegraphic communication" was made to Sheffield. Handley returned and led the passengers out of the tunnel and they walked all the way to Shepley. Railway company workmen soon arrived on the scene and began clearing the line. By 8am, the down line through the tunnel had been reopened. The Huddersfield Chronicle recorded the names of around half of the dozen-or-so passengers:
On Saturday 5 February, Edgar Wadsworth (aged 19) was travelling back on the 11:16am Sheffield to Huddersfield train with his friend John Herbert Foxton (aged 16), the son of Stamper Foxton who was the landlord of the Junction Inn, Moldgreen. The pair had the compartment to themselves and Foxton seemingly decided it would be fun to have they door open as the went through Cumberworth Tunnel. He had partially opened the door when "it suddenly jerked open" and Foxton tumbled out. Wadsworth raised the alarm when the train arrived at Shepley and accompanied the Station Master back to the tunnel, where they found the badly injured Foxton crawling out of the tunnel entrance. He was taken to Denby Dale and then on to Huddersfield Infirmary, where he died at 9:50pm. At the inquest, senior house surgeon Mr. Marshall gave evidence that Foxton's "right leg was almost entirely separated from the thigh" and it was necessary to amputate. A verdict of "accidental death" was recorded.
The body of 13-year-old Harry Brook Binns of Lockwood was found in Cumberworth Tunnel in October 1905. The teenager had run away from home earlier in the year and had been found trying to board a ship to America at Liverpool. At the inquest into his death, the jury delivered a verdict of "Found dead on the line, there being no evidence to say how he got there".
Denby Dale platelayer William Henry Hirst (aged 24) was died in Huddersfield Infirmary after being hit by a train in the tunnel at 10am on Thursday 25 February 1915. He was working with a team of men in the tunnel and had stood aside to allow a ballast train to pass by — in the brave van of the ballast train was William's father, foreman platelayer John Edward Hirst. An express train to Penistone had preceded the ballast train and the tunnel was still thick with smoke which unfortunately meant that William failed to see a passenger train coming in the direction and was hit before he could step out of the way. He died the following Monday from his injuries. A verdict of "accidental death" was recorded at the inquest and it was noted that there were no "man holes" in the tunnel in which railway workers could shelter in safety from passing trains.