The deal, for an undisclosed sum, puts an end to more than a month of speculation and transforms Blakemore into the runaway dominant force within Spar with a turnover of more than £1.1bn.
Blakemore posted turnover of £815m in 2009/10 and Capper posted a turnover of £289m.
Although Capper will trade as a separate division of Blakemore as part of the deal, the capture increases the area Blakemore serves into South Wales, Sussex, Gloucester, Oxfordshire, Kent and South London.
It previously served Spar stores in an area covering North Wales to East Anglia and North Lincolnshire to North London.
The deal now gives Blakemore a 45% share of Spar among the remaining five Spar wholesalers more than double that of nearest Spar wholesaler Henderson Group, which delivers to Spar stores in Northern Ireland. It will serve 1,096 of Spar's 2,573 stores.
"This is a great opportunity to bring two long-established, family-owned businesses together and allows us to move forward in the growing UK convenience store sector," said AF Blakemore & Son group MD Peter Blakemore.
"Blakemore and Capper & Co are similar companies that already have a shared history and a common set of values. The two businesses currently operate in regions adjacent to each other and this will allow for many benefits to be realised, particularly in areas of trading and distribution."
Capper chairman Bill Capper added: "Integration with Blakemore is the right way forward for Capper & Co. It will strengthen Spar in the UK and bring many opportunities and benefits to the business."
Capper and MD Robert Upton will now join the main AF Blakemore board of directors and all Capper's 2,418 staff will join the enlarged business.
Wholesale experts believe the deal could kickstart further consolidation between Spar wholesalers looking to forge a stronger business model. Any mergers between the remaining players would only benefit Spar, a wholesale source told The Grocer.