CAIRO—A wave of economic austerity is squeezing the Arab world’s middle class, pushing a segment of society that is key to growth and stability into making painful cutbacks and fueling discontent.

Egyptians say they are taking second jobs and dining out less often. Jordanians trying to make ends meet are pulling children from private schools. In Tunisia, hundreds of thousands of civil servants staged a one-day strike last month to demand a pay increase.

“I...