The bridge was formally opened on 19 March 1932. Amongst those who attended and gave speeches were the State Governor, Sir Philip Game, the Minister for Public Works, and Ennis. The Premier of NSW, Labor politician Jack Lang, was to open the bridge by cutting a ribbon at its southern end.
However, just as he was about to do so, a man in military uniform moved forward on horseback and slashed the ribbon with a sword, declaring the bridge to be open "in the name of His Majesty the King and the decent and respectable citizens of New South Wales". He was promptly arrested. The ribbon was hurriedly retied and Lang performed the official opening ceremony. After he did so, there was a 21-gun salute and a RAAF flypast.
The intruder was identified as Francis de Groot. He was convicted of offensive behaviour (he was fined £5)after a psychiatric test proved he was sane. De Groot was not a member of the regular Army but his uniform allowed him to blend in with the real cavalry. He was a member of a right-wing paramilitary group called the New Guard, opposed to Lang's leftist policies. This incident was one of several that Lang had with the New Guard in that year.
A similar ribbon-cutting ceremony on the bridge's northern side by North Sydney's mayor, Alderman Primrose, was carried out without incident. It was later discovered that Primrose was also a New Guard member, but his role in and knowledge of the de Groot incident, if any, are unclear