The NASA F-8 Modified was the first digital and Concorde came well before that as an analogue FBW aircraft but are we sure there weren't even earlier analogue fly-by-wire aircraft? Test flying models perhaps?
Like the modified B47 that flew with analogue FBW controls on 14 December 1967, a good two years before Concorde, there was lots of funny flight test stuff going on in the 50s and 60s.