The deal is believed to be worth in the region of £5m over three years. No further financial details have been disclosed.
Loewy has also acquired Rainier's sister agencies Lighthouse PR and Custard PR.
Loewy made its first foray into the PR sector last year when it bought consumer agency BMA Communications (PRWeek, 17 November 2005).
For more details see PRWeek later this week (27 October edition).