Born in Dunedin on 7 February 1879, Frederick Thomas Seelye was the third of five children of John Cassilis Seelye, a cloth cutter, and his wife, Amelia Elmore Jarman. He attended Mornington School, where he was dux in 1893. This was followed by three years at Otago Boys' High School, and in 1898 he began studies at the Otago School of Mines.
Seelye became interested in geology, and particularly the chemical analysis of rocks and minerals. His graduation in 1901 was followed by an appointment, in 1902, as instructor in chemistry and mathematics at the Waihi School of Mines. He was also required to analyse ores and tailings from mining operations in the area. This allowed him to further develop his analytical skills, and he became an exceptionally well-qualified analyst.
On 13 December 1911 Frederick Seelye married Flora Annabella Nicholson at Waihi. Two sons and a daughter were born before the Seelyes moved to Wellington, when Frederick took up the position of chief silicate analyst at the Dominion Laboratory in 1920.
During the 1930s and 1940s Seelye came to be recognised as the most outstanding inorganic chemist in New Zealand. He possessed great patience, concentration and manipulative skills, paid meticulous attention to detail, and had a good knowledge of the chemistry and mode of occurrence of rocks and minerals. These attributes were essential to his success in the difficult and time-consuming chemical analysis of silicate rocks and minerals. He achieved international recognition in the late 1940s when he was one of 34 analysts selected worldwide in an American-sponsored programme to test the accuracy of rock and mineral analyses. He was able to determine the presence of fluorine in one of the samples, an element missed by the majority of the participants. Seelye's analyses were described as falling into the very select group of first-class data produced by the test.
All the more remarkable is the fact that Seelye produced his analyses under conditions that today would be considered inadequate and even hazardous. He worked alone in three small rooms on the top floor of an old building. The windows were deeply etched by acid fumes because he often neglected to use the fume cupboards, which in any case were inadequate. Because of his preoccupation with his work, visitors were not always welcome in his laboratory, and this, combined with a somewhat austere, ascetic appearance, made him a formidable figure to younger members of the staff. However, he could be kind and very helpful, and was always ready to do more than required. Colleagues, notably Professor C. O. Hutton (who collaborated with him in numerous published papers), praised his skill and the reliability of his data as well as his contribution to mineralogy and petrology in New Zealand. Many times he determined rare elements that would have been overlooked by a less careful analyst. He seems to have delighted in the challenge of a particularly difficult analysis. A compilation of igneous rock analyses made between 1917 and 1957, most by Seelye, pays tribute to his contribution to geology in New Zealand.
Geology was not the only field to benefit from Seelye's skills. Industry and agriculture also relied on his analyses of industrial rocks and minerals. He analysed rocks for use in concrete and roading aggregate; iron sands and silica sands for early studies in steel and glass manufacture; clays for ceramics; limestones, phosphates and serpentinites for fertiliser; and trace elements in soils for agriculture. These and a host of other problems were all studied with the same attention to detail that characterised all his work.
Seelye officially retired from the Dominion Laboratory in 1946. However, because of the worldwide scarcity of analysts with similar skills, he continued working for a nominal allowance until 1953, when he finally retired. He was a foundation member of the New Zealand Institute of Chemistry (1931), and was elected to fellowship of the institute in 1943; on his retirement he was made an honorary life member. Wider recognition came with his election as a fellow of the Royal Society of New Zealand in 1944. Seelye was an active member of St Giles Presbyterian Church, Lyall Bay, which he attended regularly for 42 years until his death in Wellington on 1 June 1962 at the age of 83. He was survived by his wife and children.