The moments before the accident at around 2.30pm today were caught on camera by a horrified fellow driver who described hearing a loud crack.
South Africa's Society for the Prevention of Cruelty to Animals told local media the giraffe has since died and the truck driver could face criminal charges.
Engineer Thinus Botha, 32, took the photo of the two giraffes after driving next to the truck for half a mile on the N1 on the outskirts of Pretoria, South Africa's capital.
He decided to pull over to capture the moment - and witnessed the gruesome accident seconds later.
'I pulled over just before the bridge and a few seconds after I took the photo the first giraffe hit its head on the bridge,' he told MailOnline.