Place potatoes in a large saucepan and cover with water; bring to a boil. Reduce heat to medium-low and simmer until tender, about 12 minutes. Drain potatoes; refrigerate to cool.

Meanwhile, place eggs in a saucepan and cover with water. Bring to a boil, remove from heat, cover the pan, and let eggs stand in hot water for 15 minutes. Remove eggs from hot water, cool under cold running water, and peel. Chop eggs; place in a large bowl.

Stir sweet pickles, mayonnaise, and onion into eggs. Refrigerate to blend flavors, at least 30 minutes. Add potatoes; refrigerate at least 30 minutes more. Serve cold.