His first major activity on the king's behalf was in France with the king's uncle, the duke of Gloucester in June–July 1436, which had the goal of relieving Calais, in a short, sharp campaign; albeit using the largest English army seen on French soil since Henry V's campaign.
He briefly reinforced the Duke of York in Normandy, but all returned to England in late July 1437.
For this service he was granted the county of Boulogne in reward; he was not, however, to ever return, even though the earl of Warwick had named him as one of the preferred nobles to accompany him back to France that year to relieve York.
On 5 January the following year (by now a 'prominent Household servant,' according to Ralph Griffiths) he was made steward of the Duchy of Lancaster and steward of Leicester, Castle Donington, and Higham Ferrers.
In 1439 he was sworn onto the king's council, which was effectively running the country during the king's minority, and in 1446 he was 'intimately involved' in peace negotiations with the French.
 In 1445, he was appointed Lord High Constable, an envoy to France that same year beginning those negotiations, and five years later, to the Scots.

In June 1457 he was personally responsible for intervening in the activities of Bishop Pecock, a virulent anti-Lollard.
However, his virulence led to suspicions of heresy, which resulted in Beaumont's instigation of a formal examination into the bishop's sermons and writings; Peckock agreed to recant and abjured his heresy in November 1457, resigning his bishopric a year later.
His first major activity on the king's behalf was in France with the king's uncle, the duke of Gloucester in June–July 1436, which had the goal of relieving Calais, in a short, sharp campaign; albeit using the largest English army seen on French soil since Henry V's campaign. He briefly reinforced the Duke of York in Normandy, but all returned to England in late July 1437. For this service he was granted the county of Boulogne in reward; he was not, however, to ever return, even though the earl of Warwick had named him as one of the preferred nobles to accompany him back to France that year to relieve York. On 5 January the following year (by now a 'prominent Household servant,' according to Ralph Griffiths) he was made steward of the Duchy of Lancaster and steward of Leicester, Castle Donington, and Higham Ferrers. In 1439 he was sworn onto the king's council, which was effectively running the country during the king's minority, and in 1446 he was 'intimately involved' in peace negotiations with the French.  In 1445, he was appointed Lord High Constable, an envoy to France that same year beginning those negotiations, and five years later, to the Scots.
In June 1457 he was personally responsible for intervening in the activities of Bishop Pecock, a virulent anti-Lollard. However, his virulence led to suspicions of heresy, which resulted in Beaumont's instigation of a formal examination into the bishop's sermons and writings; Peckock agreed to recant and abjured his heresy in November 1457, resigning his bishopric a year later.
John Beaumont, 1st Viscount Beaumont