He was the son of a landdrost in the Orange Free State, and attended South African College School before practicing as an attorney for several years in Cape Town.
He was first elected to the Parliament of the Cape of Good Hope under the Molteno Ministry in 1875 to represent the constituency of Aliwal North, and served continuously until 1904.
Initially, due to their inaccessibility in the remote frontier mountains, most rural Xhosa people of the Cape failed to register as voters.
On 4 July 1907, together with fellow MPs Dr Antonie Viljoen and James Molteno, he supported the Cape's first parliamentary attempt to give women of all races the vote.
[4][5] At the time of the Second Boer War, Sauer was accused of fermenting pro-Boer sentiment among the Cape Dutch, though in fact he repeatedly tried to persuade his constituents to abstain from the ongoing struggle against British rule.
[6] In early 1901, Sauer travelled to London with fellow Cape politician John X. Merriman to persuade the British government not to make war on the South African Republic (Transvaal) and Orange Free State.
The House of Commons refused them a hearing, and the public meetings that they held were disrupted by increasingly large numbers of imperial demonstrators.
The concept was bitterly opposed by the representatives of the other South African colonies and their exclusively white electorate; Sauer later proposed the extension of the qualified Cape franchise to the rest of the Union.
While some of his allies thought this compromise "pathetic", Sauer believed it was the only way to retain a semblance of political voice for nonwhites, without scuppering the entire Union.