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 on Wednesday he was only full of praise for the former St Mirren midfielder's abilities.
He said: "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."
St Johnstone have 17 players whose contracts expire following the conclusion of the current campaign, and Lomas hopes that by signing up Brittain early it will save his squad from the kind of upheaval they suffered last summer.
He was forced to bring in nine new faces after losing 19 members of his playing staff.
Lomas added: "We think it's a good acquisition. The club has got a few players out of contract at the end of the season and we had to look at every situation.
"It was important that we were not caught out like last season, where we had a high turnover of players and had to bring a lot in very quickly."