Caretaker boss Guiliano Grazioli needed the Bees to triumph at Underhill and Lincoln not to win if he was to keep the club in League Two after taking over from Martin Allen last month.
And after McLeod stepped up to fire Barnet ahead they never looked in danger, with the Imps' 3-0 home defeat to Aldershot ensuring they instead suffered their first relegation from the Football League since 1987.
Mark Marshall caused the Vale backline problems early on and was unlucky not to score after 19 minutes when his stinging 20-yard effort from the left was brilliantly parried by Chris Martin.
And the former Swindon winger came close again when he dispossessed Ritchie Sutton with a superb sliding tackle but his curling shot shaved the outside of a post.
It took until the third minute of the second half for the home side to reap their reward when McLeod smashed home a penalty after he was brought down by Gareth Owen. Sam Walker was called into action in the final moments to keep the Bees ahead when he saved at the feet of Marc Richards.