The protest was called by Tunisia ' s ruling Islamist Ennahda party.
Waving the flags of both Tunisia and Egypt, which both saw long - standing autocratic regimes toppled in Arab Spring uprisings, demonstrators thronged the city center.
" Down with military power! " and " No to the force of arms, yes to the ballot box! " and " The people want Morsi back! " were among slogans they chanted.
Speakers at the rally roundly denounced Egypt ' s Tamarod(Arabic for Rebellion) movement whose massive mobilization of the people led to Morsi ' s eventual downfall.
They also shouted slogans against Egyptian military chief General Abdel Fattah al - Sisi.
" This military coup was inspired by outside parties and aims to overthrow Arab Spring Islamist governments, " said protester Salem Achour, 42, draped in Egypt ' s colors.
" It ' s a war against Islam. "
One speaker spoke to demonstrators through a loudhailer, addressing Morsi supporters who have been gathered for days at the Rabaa al - Adawiya mosque in Cairo.
" We call on our Egyptian brothers at Rabaa al - Adawiya to stand firm until victory, " he shouted.
There was a heavy security presence in central Tunis for the authorized protest, after permission for a previous pro - Morsi demonstration organized by Ennahda was rejected last week.
The day after the July 3 coup that toppled Morsi, the opposition party Nidaa Tounes demanded the departure of the ruling Islamists in Tunisia and a government of national unity.
A Tunisian Tamarod movement on July 4 launched a petition calling for the dissolution of the National Assembly.
President Moncef Marzouki has ruled out the risk of Tunisia ' s elected authorities being deposed in the wake of Morsi ' s ouster, but also stressed the need to " pay attention " to popular demands.