The 45-year-old won 21 caps for Wales in Rugby Union and later became a dual international after switching codes to Rugby League.
He spent six seasons coaching the Scarlets alongside Gareth Jenkins, Phil Davies and then Nigel Davies between 2003 and 2009 and has most recently been at the helm of Cardiff RFC in the Principality Premiership.
Moriarty already has a close relationship with Tait, who took over from Steve Bates at the Flacons last month, having played with the Scotland and Lions star in a highly successful Widnes Rugby League team that was crowned World Club Champions in 1989.
"I've known Alan Tait for many years, right through from our time at Widnes in 1989 to the present day, and we've always kept in touch," said Moriarty.
"We always got on very well at Widnes, probably for the simple reason that we say it as it is. There are people out there who don't like it that way sometimes, but we're two very driven and like-minded personalities. We want people around us who share the same standards and mentality, and Alan knows
that's what he's getting with me.
"Even when I was with the Scarlets we would meet up whenever we played the Scottish teams, and he would often ring me to ask my opinion about guys playing in Wales that he might have been looking to sign.
"Obviously the situation has changed at Newcastle now with Alan becoming the head coach, and from my own perspective for the last year or so I'd really been looking for a new challenge outside of Wales. It's a chance for me to broaden my career and my perspective in a different environment.
"The sides that I've been involved with, Swansea and the Scarlets, have probably been the two most entertaining teams that have been around in Welsh rugby during that period. I know exactly what's required, and how the game is supposed to be played. I've already had the discussion with Alan, and hopefully that's the direction we can get the team going in.
"With Alan being a back and myself being a forward, the natural order of things is that my work will be predominantly with the pack. That's not to say that there won't be any cross-over though. I'm equally at home working with backs, and I see myself and Alan dove-tailing quite well whichever players we're working with."
Tait clearly has huge respect for his former Rugby League colleague, a man who enjoyed substantial success at both club and regional level as a coach after a truly distinguished playing career.
During his time with the Scarlets, Moriarty helped the region claim a Magners League crown and reach the last four of the Heineken Cup and Tait would love to see that sort of success arrive at Kingston Park.
"He has been there and done it at a high level over a considerable period of time, he brings the fresh ideas that we need and I believe he can really help us drive this talented group of players onto the next level," added Tait.
"As a newcomer to the head coach's role I was adamant that I wanted an experienced number two to help me along, and Paul is definitely someone who ticks that box.
"He is very highly regarded in the game, and during his time at the Scarlets he has helped them win the Magners League title as well as reaching the Heineken Cup semi-finals. Those are the sorts of standards we want to build towards, and Paul offers us some valuable outside input as well as his undoubted quality as a proven coach."