The deal to supply fresh salmon and haddock is worth around £400,000 a year to the company, based near Linlithgow, West Lothian.
Deliveries are made daily into dozens of Aldi stores across Scotland.
Campbells said its upgraded facilities allowed it to pack fish more efficiently as well as offering a better quality of final packaging.
It is soon to begin supplying cod to Aldi and is considering offering several other white fish in the future.
Steven Walker, director at Campbells, said: "With our upcoming plans to supply Aldi with even more fish, it made sense for us to focus our plans on improving our packaging processes, helping to make our business more efficient while improving the look and accessibility of our products.
"As well as our plans to supply cod to Aldi, we are also looking into the possibility of adding coley, hake, ling and pollack to the range making it easy for consumers to enjoy fresh fish from around Scotland.
"Our relationship with Aldi is of great importance and we look forward to working with them and growing our relationship."
There are 36 people working in the Campbells seafood division, working in areas ranging from hand filleting to packaging.
Richard Holloway at Aldi said: "We're committed to building relationships with the best Scottish suppliers in order to provide our customers with quality produce at everyday low prices.
"Working with suppliers like Campbells helps us to deliver this to our customers day in and day out."
Campbells also supplies meat to a number of leading Scottish chefs including Tom Kitchin and Martin Wishart as well as restaurants and hotels across Scotland.
It also makes haggis and black pudding, under the Nick Nairn brand, for supply into supermarkets.
Restaurants, hotels, pubs, the NHS, universities and schools are also among its customers.
Its most recent accounts, for 2012, showed turnover of £50.75 million and pre-tax profits of £827,901.
The company can be traced to Thomas Campbell opening a butcher's in Edinburgh in 1910.
The modern business was started in 1972 by his grandson Edward.
Edward's son Christopher is the current managing director.
The company's former site at Broxburn, West Lothian, was destroyed by fire in May 2009 but it opened in Linlithgow a few months later.