Lord of Thomond in Connaught, Knight, Constable of Colchester Castle (in right of his wife), Stewart of the Forest of Essex, King's Lieutenant in Gascony, Governor of London, Warden of the Forest of Dean, Constable of St. Briavels Castle. 
Thomas, with his brother Gilbert, was knighted by Simon de Montfort, Earl of Leicester before the Battle of Lewes 14 May 1264. They were fighting against King Henry III.
Before 18 February 1275, Thomas married "Juliane Fitz Maurice, daughter and co-heiress of Maurice Fitz Maurice Fitz Gerald, Knight, 4th Baron of Offaly, Justiciar of Ireland, by his his first wife, Maud de Prendergast." 
Thomas and Juliane had three sons and two daughters:
Gilbert, who was knighted
Richard, who was knighted
Richard, called 'Master'
Margaret, married Gilbert de Umfreville andBartholomew de Badlesmere
Thomas de Clare died in Ireland on 29 aug 1287.
Footnotes and citations
↑ 1.01.11.21.22.214.171.124.7 Douglas Richardson, Royal Ancestry: A Study in Colonial and Medieval Families, 5 vols., ed. Kimball G. Everingham (Salt Lake City, Utah: the author, 2013), Vol I, p 216, BADLESMERE #8.
↑ Douglas Richardson, Royal Ancestry: A Study in Colonial and Medieval Families, 5 vols., ed. Kimball G. Everingham (Salt Lake City, Utah: the author, 2013), Vol. II, p 194, CLARE #7ii.
The complete Peerage of England, Scotland, Ireland, Great Britain, and the United Kingdom, extant, extinct, or dormant, Cokayne, George Edward, (Gloucester [England] : Alan Sutton Pub. Ltd., 1987), 942 D22cok., vol. 1 p. 149