The supermarket has handed key briefs to Hill & Knowlton and Cake as it attempts to build on a rise in sales announced this week.
The two agencies will support brand strategy and media campaigns.
Meanwhile, Camron PR will take on homeware and general merchandise and Modus Publicity will manage PR for clothing.
Finally, BeautySeen will assume responsibility for health and beauty.
Hill & Knowlton was the only consumer agency Sainsbury's previously worked with on a formal basis.
Rachel Friend, head of consumer PR, commented: 'I now believe we have the right framework of agency support to deliver cut-through consumer PR.' Friend arrived at the supermarket in February, having previously been head of consumer PR at H&K.
This week, Britain's third largest supermarket announced a rise in quarterly sales at the top end of analysts' expectations, despite a reduction in market share.
Sainsbury's will continue to use Finsbury for financial PR and Fishburn Hedges for public affairs.