Laird had worked at Consolidated for the past decade and was part of the team that undertook the agency's management buyout in 2001.
She left Consolidated in July and had several weeks off before starting work at the mobile phone firm.
Consolidated managing director Sarah Robinson said Laird's exit was amicable, adding: ‘Rachael felt she wanted a new challenge. We remain on excellent terms.'
Laird is the second senior exit from Consolidated in recent weeks. PRWeek broke the news last week that director Paul Davies is to join rival The Red Consultancy (PRWeek, 1 September).
Laird will not be directly replaced at Consolidated, where her major accounts such as Buena Vista Home Entertainment and Budweiser have been handed to fellow board director Chris Lawrence and associate board director Rose Davidson.
At Motorola, she has replaced Una Kent, who remains with the company but has relocated to Australia to head its high-growth markets division as PR director.
Motorola, the world's second largest maker of mobile phones, recently posted a 48 per cent rise in second-quarter earnings on the back of record handset sales, in particular for its Razr brand.
Razr has been caught up in controversy over an ad campaign featuring fashion duo Dolce & Gabbana. The print ads show Domenico Dolce brandishing the handset like a flick knife. The Advertising Standards Authority received 100 complaints and launched an inquiry.