Thomas was born on December 24th, Christmas Eve, 1822 in Edinburgh, Midlothian, Scotland. He was the third son of Thomas (Neilson) and Margaret (Black) Nelson.

Thomas was educated at the high school in Edinburgh, then joined his father's publishing firm in 1839.

In 1841, Thomas was living with his parents and five of his siblings in the afternoon shade of Edinburgh Castle at 398 Castle Hill in Brown's Close.

In 1850, Thomas devised an improved rotary printing press.

On census day in 1851 (March 30th), Thomas, his parents, and his sisters Ann and Janet were listed as visitors in the home of his brother John in the Manse of the Free Church of Newport, Forgan Parish, Maryton, Fife where he (John) was a minister.

Thomas' father went to be with The Lord in late March of 1861. He was laid to rest in the Grange Cemetery in Edinburgh, Scotland.

In April of 1861, Thomas was living with his mother and two of his siblings, Ann and James in the house his father had built. Thomas and James had taken over their father's business and were listed as publishers. The family had three servants.

Thomas married Jessie Kemp in Edinburgh on April 30th, 1868.

Thomas and Jessie had five children:
-Margaret Edith Stuart (b. 1870, Edinburgh)
-Mary Elinor (b. 1872, Edinburgh)
-Thomas Graeme (b. 1874, Edinburgh)
-Thomas Arthur (b. 1876, Edinburgh)
-Ian Theodore (b. 1878, Edinburgh)

Thomas and Jessie's son Thomas Graeme was called home at a very young age when he passed away on June 19th, 1876. He was only 18 months old. He was laid to rest in the Grange Cemetery in Edinburgh, Scotland.

Thomas' mother went to be with The Lord in mid-December of 1877. She was laid to rest in the Grange Cemetery in Edinburgh, Scotland.

Thomas passed into eternity October 20th, 1892 in Edinburgh, Scotland. He was laid to rest at Grange Cemetery, Edinburgh, Scotland among his family.