On her father's death in 1234, he acquired her share of the paternal inheritance, which consisted of the hereditary office of Constable of Scotland and one-third of the lordship of Galloway.

Further unrest in 1247, possibly due to his strict rule, found de Quincy trapped in a castle, from which he escaped to obtain help from King Alexander in suppressing the rebellion.

[2] In England he also steered clear of politics initially but was gradually drawn into the baronial opposition to the rule of King Henry III, He joined with other nobles in 1239 and 1246 in written remonstrances to the Pope about papal interference in English affairs.

In 1258, he was elected by the barons to the twelve-member commission charged with overseeing the revised constitution of the Provisions of Oxford and was appointed also to the committee to arrange the financial aid promised to Henry.

In 1259 he led a delegation to St Omer that forbade the King's brother Richard, Earl of Cornwall from returning to England unless he swore to observe the Provisions of Oxford.