Delve spent much of last season leading the side in the absence of the injured Stirling Mortlock and has been handed the top job by coach Damien Hill after turning his back on an offer to play in France to extend his stay in Super Rugby.
Delve was called-up to help out the Welsh squad in Australia last year when injuries struck, playing in the midweek game against the Brumbies, but hasn't figured in Test rugby since 2010.
He will lead the Rebels in their final friendly this weekend before the Super Rugby season kicks-off and it is not beyond the realms of possibility that if he plays well enough he could come onto Warren Gatland's radar for this summer's Lions tour.
"His performances on and off the field have been recognised by the playing group and the whole organisation and it's a fantastic achievement. Gareth's consistently been one of the leaders of the team," said Hill.
Delve said he didn't expect the honour when he arrived at the new club three years ago having never played Super Rugby. The 30-year-old had previously played for Bath, Cardiff Blues and Gloucester.
"The club's been fantastic in giving me the opportunity to have a leadership role and being a part of building a great culture at this place. This is icing on the cake," said Delve.
"It's an incredible honour and not one that I expected when I turned up three years ago as a foreign player. We want to play with flair, we want to play with excitement and I need to try and lead the way."