The McDiarmid Park boss has swooped early to tie up the Staggies skipper on a pre-contract agreement.
The pair were involved in a spat earlier this season when Lomas accused Brittain of diving to get one of his players sent off in Saints' 2-1 win at the Global Energy Stadium in September.
He branded the 29-year-old a "cheat", but was only full of praise for the former St Mirren midfielder's abilities.
He told Press Association Sport: "We have agreed a deal with Richie. It is a good deal for the club and we are delighted to get him.
"He will bring good experience to the club and great quality from dead-ball situations. He's also a fantastic leader and has shown that as captain of Ross County.
"Richie was a very young player at St Mirren and it showed character that he was prepared to drop down a level and develop.
"He has come back a stronger player and showed that he belongs in the SPL."