Sir Thomas Kay Sidey (27 May 1863 – 20 May 1933) was a New Zealand politician from the Otago region, remembered for his successful advocacy of daylight saving time.

His father had come to wealth during the Otago gold rush as a storekeeper.

[1] Sidey was elected to the House of Representatives in the Caversham by-election as an independent liberal in 1901.

His widow, Helena, Lady Sidey, was appointed an Officer of the Order of the British Empire for social welfare services, especially in connection with women's organisations, in the 1953 Coronation Honours.

[5] The Royal Society of New Zealand awards the T. K. Sidey Medal at irregular intervals for "outstanding scientific research".