Holmes, 27, scored 24 tries in three seasons for Leicester but has now moved to Wales in order to continue his hopes of playing Test rugby for Wayne Pivac’s side.
Had he stayed with Leicester, Holmes would have been unavailable for internationals due to the Welsh Rugby Union’s eligibility laws.
“Jonah is a big signing and, of course, you only have to look at what Sam (Davies) did last year,” said Dragons assistant coach Barry Maddocks, speaking on the rugby podcast for BBC Cymru.
“He’s made an excellent impression at the region and made a real difference to the group.
“We had that leadership and experience off someone like Sam and Jonah will once again bring that from where he has been playing.
“He can play in multiple positions too which will be very important. Everything is looking very positive going forward.”
Holmes has three caps for Wales to date.
Qualifying to wear the Three Feathers through his Welsh-born grandmother, he was a surprise selection for the November of 2018 and made his Test debut at full-back in a hammering of Tonga.
In 2019 he made two further appearances, starting the Six Nations win over Italy in Rome before appearing in the World Cup warm-up clash with Ireland in Cardiff.
Maddocks believes the signing of players such as Holmes can help the Dragons continue their upward curve under director of rugby Dean Ryan.
“This is my fourth season here and last year we made a big leap forward,” he said.
“The plan now is to have players like Jonah and a couple of other players come in and make an impact. It’s starting to progress and get to the point where Dean sees the Dragons going forward.”
The Dragons are set to return to action in the Guinness PRO14 on August 22.
“The players have all been great,” Maddocks said of how the Dragons have coped during lockdown.
“Someone like Ollie Griffiths can’t stop. He always has to be doing something all the time, lifting weights or going for a run. The hard part to begin with was not knowing when we would be back.
“It now looks like an August playing return now so at least there is that starting point for everyone to look at.”
