I just played a game of CTF where a high elo Widow was wrecking my team, so I had to switch to Sombra to deal with her. I ended the game with 93% kill participation. I have never seen that in my 10 months of playing Overwatch and watching T500 streams regularly. Has anyone gotten any higher than this?
Probably doesn’t count, but: pre-nano boost buff. I had this Genji on my team that always managed to pull off amazing blade kills (one of them a team wipe). I nano’d him around four times and he got 75% kill participation if I remember correctly. Because of me, mind you. 
It’s not much, but I’m proud of my pet Genji.
Not exactly relevant but my friend got a card saying: “21 rocket direct hits. 117% of Rockets Fired”
here’s the link to the video if interested https://www.youtube.com/watch?v=gv5q2vb6nXA
Waaaay back in the early days there was a screenshot of 5 lucio’s speedboosting and healing a zen who at the end had a 100% kill participation. miss those times
In team deathmatch because the matchmaking is so bad you could get 100% kill participation as Tracer when you got a team that stuck together.
No Limits is still the daily mode!
In a normal competitive match i had 73% kill participation with Tracer. Granted i only play in plat, but i still was proud!
I think I’ve seen an 87% percent once as Zenyatta when my discord game was on point.
I got 120% in a custom game once. Even got an endgame card showing it.
https://i.imgur.com/9pO59Ii.jpg
I had 100% kill participation as Brig in a 2 minute game.
My favourite card has to be 96% time on fire
https://i.imgur.com/u8712m8.jpg
With my second favourite, the lesser known multikill card where i don’t think I’ve even seen since
https://i.imgur.com/LIP94v8.jpg
I think i had something near that. Its a very vague memory, from season 5 or something when i mained Pharah. But i had 81 elims and like 90% KP
MVP is my favorite card to get. I think my record is 92% of the match on fire.
I had once 82% kill participation as D.Va.
My friend had one game where he was on fire 94% of the time with Brig, but we are pretty sure the game must have bugged out… 
I don’t think so. Brigitte is, well, you know. She has the highest on-fire percentage from all the characters, because she does her balanced thing.
True, but he did die a couple of times - surely that alone would have pulled down the fire rate?
When for some reason i’m playing well, the fire meter just refuses to lower when I die. Could be the reason your friend had such a massive on-fire rate.
I just checked, it was actually 96%. 
If you keep killing 3 per life, you can die. I was on fire that whole game in spite of dying 3 times.
What map it was? King’s Row?