The Cork-born prop made 78 appearances for Harlequins over the past three years, establishing himself as a standout performer for the Londoners in the Guinness Premiership.
His progression through to the Ireland senior squad was preceded by nine appearances for Ireland 'A', but he knows that that international recognition will count for little as he prepares to challenge some big names for a place in the Leinster front row.
Commenting on his move back across the Irish Sea, Ross said: "I'm very pleased to be joining Leinster at what is a hugely exciting time for the province.
"Leinster are a successful team with a strong winning culture and they have proven that over the last few years.
"It's an incredible opportunity for me to come back to play in Ireland, but I know that the competition will be intense to get into the starting line-up with CJ (van der Linde) and Stan (Wright) here already.
"It's a challenge that I'm looking forward to and hopefully I can build on my two Ireland appearances earlier this summer, but first and foremost I will have to work hard to break into the Leinster team."
Ross, who played underage rugby for Fermoy RFC and for UCC and Cork Constitution at club level, gained his first Test cap off the bench in May's win over Canada in Vancouver.
A week later, he wore the number 3 jersey as Ireland rounded off the tour with a 27-10 victory over the USA in Santa Clara and a call-up to last month's training camp in Belfast followed.
The move to Leinster gives him a chance to further his international claims, with the prospect of regularly playing against a number of his rivals for the Ireland shirt over the coming seasons.
The 29-year-old added: "I owe a great deal to Harlequins for the chance that they gave me, but I felt that now was the right time to return to Ireland and I hope that we can go on and bring even more success to Leinster this season."