It may be that the tradition of Henry's riotous youth, immortalised by Shakespeare, is partly due to political enmity. Henry's record of involvement in war and politics, even in his youth, disproves this tradition. The most famous incident, his quarrel with the chief justice, has no contemporary authority and was first related by Sir Thomas Elyot in 1531.

Henry tackled all of the domestic policies together and gradually built on them a wider policy. From the first, he made it clear that he would rule England as the head of a united nation. On the one hand, he let past differences be forgotten – the late Richard II was honourably re-interred; the young Mortimer was taken into favour; the heirs of those who had suffered in the last reign were restored gradually to their titles and estates. On the other hand, where Henry saw a grave domestic danger, he acted firmly and ruthlessly – such as the Lollard discontent in January 1414, including the execution by burning of Henry's old friend Sir John Oldcastle in 1417, so as to "nip the movement in the bud" and make his own position as ruler secure.

Less than three years later, Henry was in command of part of the English forces—he led his own army into Wales against Owain Glyndŵr and joined forces with his father to fight Henry "Hotspur" Percy at the Battle of Shrewsbury in 1403. It was there that the sixteen-year-old Prince was almost killed by an arrow that became stuck in his face. An ordinary soldier might have died from such a wound, but Henry had the benefit of the best possible care. Over a period of several days, John Bradmore, the royal physician, treated the wound with honey to act as an antiseptic, crafted a tool to screw into the broken arrow shaft and thus extract the arrow without doing further damage, and then flushed the wound with alcohol. The operation was successful, but it left Henry with permanent scars, evidence of his experience in battle. For eighteen months, in 1410–11, Henry was in control of the country during his father's ill health, and he took full advantage of the opportunity to impose his own policies, but when the king recovered, he reversed most of these and dismissed the Prince from his council.