The Belfast opening will be the first by Di Maggio's outside Scotland.
The company, which employs more than 480 people and also plans to expand in its home city of Glasgow, more than trebled its pre-tax profits to about £1.4 million in the year to April 2012, from £419,060 in the prior 12 months. This increase was achieved on the back of a £2.6m increase in turnover to £21.27m.
Part of the jump in profits reflected a fall in directors' remuneration to £1.659m in the year to April 2012, from £2.29m in the prior 12 months.
However, a strong rise in underlying profits is evident in a jump in pre-tax profits, before directors' pay, from £2.7m to more than £3m.
Co-founder Mario Gizzi highlighted a decision by Di Maggio's to focus on providing "real value for money" through the economic downturn.
Di Maggio's, founded by Mr Gizzi and Joe Conetta, opened Italian-American restaurants in the west end of Glasgow and in Shawlands on the south side of the city in 1985. These remain popular restaurants, nearly three decades later.
While expanding this Di Maggio's branded chain over the decades, the company has also diversified, with its Cafe Andaluz tapas eateries, and Amarone Italian restaurants. It also has Barolo Grill in Glasgow, known formerly as L'Ariosto. It currently has 19 restaurants in Scotland, and has made big moves in Edinburgh in recent years with the opening of Amarone and Cafe Andaluz restaurants.
The company has revealed plans to invest a total of £1.5m in opening Cafe Andaluz and Amarone restaurants in Aberdeen, which is enjoying better economic times than many other parts of Scotland.
Di Maggio's, now owned by its two co-founders and by Joe Conetta's son, Tony, will also open a "food court" restaurant in the Castle Court shopping centre in Belfast in June, creating 20 jobs.
Mr Gizzi said: "We're encouraged by the increasing popularity of our restaurants' approach – tasty food in relaxed, comfortable surroundings at keen prices.
"The economic climate is undoubtedly challenging but people still want to have a great night out – albeit without it breaking the bank. We took a conscious decision to focus on giving real value for money to our customers and they obviously like what we're offering them."
Di Maggio's is also planning to expand its "Pinto" Mexican "street-food" concept. It has a Pinto restaurant in Queen Street in Glasgow, and plans to open a further two of these takeaway and fast casual dining outlets elsewhere in the city.
The highest-paid director of Di Maggio's, believed to be Mr Gizzi, received remuneration of £822,000 during the year to April 2012. In the prior financial year, the remuneration of the highest-paid director was about £1.05m.
Di Maggio's is still planning to open an American-style chop house in Glasgow. And it continues to look for opportunities to move into England at some stage.
Mr Gizzi said: "Although we've now been running for three decades, we're still ambitious and continue to see lots of opportunity for expansion. There are a number of sites where we're in discussions with landlords about opening restaurants under our existing brands, both in Scotland and down south and we're always looking at the next concept to ensure we stay ahead of the game."
He added that the firm's banker, Clydesdale Bank, was "extremely supportive" of its growth plans.