Marshall attended Ballymena Academy, before joining Ballymena RFC and earning a place in the Abbey Insurance Ulster Academy.
He enjoyed a breakthrough season in 2010/11, representing Ireland U20s and also making his provincial debut in October 2010, against Munster.
His rapid rise with Ulster was rewarded with a call up to the Irish squad for the 2012 Autumn Series and a few months later, Marshall made his senior international debut in the 2013 Six Nations Championship game versus Scotland. He has since added a further 10 caps to his name.
To date, Marshall has scored 21 tries in 111 appearances for his Province.
Herring joined Ulster in 2012 and made his debut in August of the same year, against Glasgow. The South African born hooker has made 129 appearances for Ulster and captained the side on numerous occasions during the 2015/16 and 2016/17 seasons.
The 27-year-old made his international bow for Ireland in June 2014 in a Summer Tour match versus Argentina. He earned two more caps earlier this month, making a try-scoring contribution in the historic 38-3 win over South Africa.
Treadwell moved to Ulster ahead of the 2016/17 season, having come through the ranks at Premiership club Harlequins.
He represented England at U20 level but qualifies for Ireland through his Irish mother. An impressive debut season with Ulster led to a call up to Joe Schmidt’s senior Ireland squad earlier this year. The powerful lock played twice against Japan in June and added a further cap, against Fiji, on 18th November.
Commenting on the new deals, Les Kiss said:
“Luke has been one of our most consistent players in recent years; he’s a robust presence in our midfield and is a brilliant link man in both attack and defence.
“He is a passionate about rugby in Ulster and I think that is evident not only in his performances on the pitch, but also in the way he contributes so positively to the local rugby community.
“Rob and Kieran have also been in excellent form this season and I was delighted to see them earn recalls into the national squad for this month’s fixtures.
“Rob has really grown as a player since his arrival at Ulster five years ago and he is widely regarded as a highly skilled hooker who leads from the front.
“Kieran has made a big impression over the past 18 months and it’s evident that he possesses all the attributes required to become a top class second row; he’s a big, mobile unit and is a good student of the game.
“All three players are determined to continue to work hard to improve and that is exactly the type of culture that we’re trying to build here.
“With increasing player movement, it’s vital that we continue to retain our best talent, and to have Luke, Rob and Kieran commit to long-term deals is a huge boost for us. They will play central roles in our programme over the next few years.”