What role does sulfuric acid play in the titration of oxalic acid and potassium permanganate?
The used analytical reaction of purple permanganate to colourless $\ce{Mn^2+}$ occurs under acidic conditions:

$$\ce{MnO4- + 8H+ + 5e- &lt;=&gt; Mn^2+ + 4H2O}$$

Under neutral conditions, permanganate would be reduced to dark brown manganese(IV) oxide:

$$\ce{MnO4- + 4H+ + 3e- &lt;=&gt; MnO2 + 2H2O}$$

Therefore, sulfuric acid is added to make the solution acidic. Actually, excess acid is required since $\ce{H+}$ is consumed during the reaction (8 mol $\ce{H+}$ per 1 mol $\ce{MnO4-}$).

Sulfuric acid is used because it is stable towards oxidation; whereas, for example, hydrochloric acid would be oxidized to chlorine by permanganate.