The definition of stalwart is a description for someone who is loyal and strong or for something that is reliable and sturdy. An example of stalwart is a description for a loyal supporter of a cause. Stalwart is a loyal and reliable supporter. An example of a stalwart is someone who has been a long time loyal supporter of a cause. 1  strong and well-built; sturdy; robust. 2  brave; valiant.  resolute; firm; unyielding.