The Aegis-owned agency beat off competition from Mediaedge:cia in the final round, while PHD and ZenithOptimedia were involved earlier in the six-month-long pitch.
Andrea Ragnetti, chief marketing officer of Royal Philips Electronics, said Carat demonstrated a commitment to creativity and a unified sense of direction.
"Carat has taken bold and tangible steps forward to approach the account with a different view on media innovation," Ragnetti said.
Philips did not reveal its total media budget, but some reports have estimated it as high as $600m, (£303m), with the majority of spend in the US. The account is worth about £7m in the UK, according to Nielsen Media Research.