Dave Masterman and Ed Edwards join BBH after a four-year stint at Fallon.
The pair won a D&AD Pencil for their "the love of live" work for Radio 1 and have won a bronze and a silver Lion at Cannes.
They have also worked on the Ben & Jerry's, Green & Black's, Skoda and Sony accounts. Before Fallon, the duo worked at DDB London.
O'Keeffe said: "We have won loads of new business and have to maintain our creative reputation. It is up to us to get the people in who can make that happen. It is not so much their awards that impress me, it is more the fact that they have produced great work for big brands."
Meanwhile, George Prest and Johnny Leathers are set to leave BBH for Lowe. The pair's credits include the controversial full-page press ads for Barnardo's, one execution of which featured a baby with a cockroach in its mouth.
They have also worked on the Xbox, Levi's and Castlemaine XXXX accounts.
Ed Morris, Lowe's creative head, said: "They used to work for me at BBH and I thought then that they were bright, intelligent and keen. Over the years, I have seen them turn from junior into mature creatives. They have got strong years to come and a lot to offer us."
Morris has a host of briefs prepared for Leathers and Prest for brands such as Olympus and Stella Artois.