After Jason Scotland had given Ipswich a first-half lead, an error from Smith allowed Leeds to poach an equaliser through Robert Snodgrass.
But, after former Ipswich defender Alex Bruce had been sent off for a second yellow card, Smith was afforded the freedom of the Leeds penalty area to head home the winner.
Smith was never meant to start the game, but had to replace Darren O'Dea who was injured in the warm-up.
Source: PA