The more I look at the list of qualities associated with the Slug Club the more I think that Harry's parents - and probably some of their friends - must have been part of it.

[Slughorn] also likes the company of the famous, the successful and the powerful. He enjoys the feeling that he influences these people. He has never wanted to occupy the throne himself; he prefers the back seat – more room to spread out, you see. He used to handpick favourites at Hogwarts, sometimes for their ambition or their brains, sometimes for their charm or their talent, and he had an uncanny knack for choosing those who would go on to become outstanding in their various fields. Horace formed a kind of club of his favourites with himself at the centre, making introductions, forging useful contacts between members, and always reaping some kind of benefit in return, whether a free box of his favourite crystallised pineapple or the chance to recommend the next junior member of the Goblin Liaison Office."
_{(Half-Blood Prince, Chapter 4, Horace Slughorn).}

• James Potter came from a super-rich family with a knack for inventing the next great bestseller in potions.


• Sirius came from an ancient pureblood family with excellent connections.


• Lily didn't come from a well-known wizarding family but was basically his favourite student.

None of these three were stupid. In fact, all of them are described as being extremely bright. If it hadn't have been for the war they would no doubt have had glittering careers before them.

We know that Slughorn was at Hogwarts at the time. Did he recruit James, Lily or Sirius to the Slug Club? Why/why not?

This prop image of the Slug Club (seen in the background of Slughorn's study) includes Lily Evans.

Another photo contains a young Lucius Malfoy

_{^{Prop photos courtesy of Warner Bros. TheRoadtoHogwarts website}}

Lily was probably in the Slug Club.

Slughorn says Lily was one of his favorite students, and speaks very kindly of her. He says she was excellent in his class, and presumed Harry had gotten his skills at Potions from her instead of Snape's notes in his textbook.

“Humph. Yes, well. You shouldn’t have favourites as a teacher, of course, but she was one of mine. Your mother,’ Slughorn added, in answer to Harry’s questioning look. ‘Lily Evans. One of the brightest I ever taught. Vivacious, you know. Charming girl.”
Harry Potter and the Half-Blood Prince

The only reason why Lily wouldn't be in the Slug Club is if she chose not to be. That also seems somewhat unlikely, as Slughorn would be unlikely to speak so warmly about someone who rejected his offer unless she did it very carefully so not to make him feel bad.

Whether James would be is less clear.

Slughorn does mention James and remembers teaching him, but doesn't speak nearly as warmly of her as he does of Lily.

James's most noticeable talent was probably Quidditch, since that's what everyone seems to mention about him first. He did seem to consider Quidditch a skill worthy of inclusion; unless he coincidentally chose her for another reason, Gwenog Jones, as the captain of the Holyhead Harpies, was in the Slug Club.

“And at the back – you’ll see her if you just crane your neck – that’s Gwenog Jones, who of course captains the Holyhead Harpies … people are always astonished to hear I’m on first-name terms with the Harpies, and free tickets whenever I want them!”

Sirius is also less clear.

As a member of a pure-blood family, and therefore also likely being thought of as having important connections, Sirius was likely at least considered by Slughorn. Slughorn does refer to him as a talented boy, but there's nothing really indicating he actually joined.

“The whole Black family had been in my house, but Sirius ended up in Gryffindor! Shame – he was a talented boy. I got his brother Regulus when he came along, but I’d have liked the set.”

In addition, Slughorn mentioned Regulus, Sirius's brother, as being a member of his club, but doesn't also mention Sirius as one.

It's possible that Slughorn invited Sirius, but Sirius declined, since it doesn't seem like something that he, as a rebel who wanted no part of wizarding high society, would want to take part in.

I think the only reason to believe they were not in it, would be personality. We have some definite facts on this subject.

We know that the Slug club existed both before and after they Lily and James were at Hogwarts. Voldemort himself was part of it, very early on, which would be roughly 50-60 years ago from the HBP. We also know that Gwenog Jones (captain of the Holyhead Harpies), was also involved in the Slug Club. Gwenog was born in 1968, while James and Lily were born in 1960.

Gwenog Jones Wikia Entry

So, the question is whether or not James, Sirius and Lily would have been invited. Slughorn says that Lily was one of his "all-time favorite students", and he is courteous enough to overlook her being muggleborn because she was so talented. James, a wealthy descendant of the Peverells (not to mention talented student/quidditch star) would have likely garnered an invitation. Sirius, a Pureblood from an old and rich wizarding family (also a talented student), also was probably on Slughorn's list.

When it comes down to personality it is less clear. Sirius tries as much as possible to distance himself from his family, so he may have distanced himself from Slughorn. Slughorn may have even decided not to have him be part of it, based on his attitude. (Think about Belby, who admits his father doesn't get along well with his famous uncle, and is never seen in the Slug Club again). After seeing that Sirious is unwilling to use his family as a leg up, he may have been passed over for the club, despite his talent. And, based on their friendship, I doubt either would go to Slughorn's parties without the other, they were somewhat of a package.

We know that Lily, gave Slughorn cheeky answers when told she should have been in Slytherin, but I doubt she would have been quite so rude as to decline the occasional party. I am willing to believe that should would have been part of the Slug Club, but there is no proof of that in the books.

And, of course, people like Lupin and Wormtail would have been passed over completely, Lupin has no connections and Wormtail is a useless weenie at best.

Lily was definitely in the Slug Club as Slughorn himself said this on many occasions (in the book The Half-Blood Prince) to Harry that she was his favorite student. However in the book there is no mention of James or Sirius ever being in the Slug Club. They surely were talented enough to be in it but as we have seen from book 5 that they were troublemakers like the Weasley twins, maybe that's the reason they never got an invitation from him (not that either one of them would have been interested to be honest). BTW this makes me think, can anyone decline the offer to join Slug Club?