Edward I knighted Guy de Beauchamp at Easter 1296. Warwick's career of public service started with the Falkirk campaign in 1298. Here he distinguished himself, and received a reward of Scottish lands worth 1,000 marks a year. At this point his father was already dead, but it was not until 5 September that Guy did homage to the king for his lands, and became Earl of Warwick and hereditary High Sheriff of Worcestershire for life. He continued in the king's service in Scotland and elsewhere. In 1299 he was present at the king's wedding to Margaret of France at Canterbury, and in 1300 he took part in the Siege of Caerlaverock Castle. The next year he was a signatory to a letter to the Pope, rejecting Rome's authority over the Scottish question, and also participated in negotiations with the French over the release of the Scottish king John Balliol. He was present at the Siege of Stirling in 1304, serving under Edward, the Prince of Wales. In March 1307 he made preparations to accompany Prince Edward to France, but this journey never took place.