An Egyptian presidential statement by spokesman Bassam Radi said the Qatari ruler's pledge came during talks in Doha with Mr El Sisi, who is on the second day of a landmark two-day visit to the Gulf Arab nation.
The visit, the first by the Egyptian leader since taking office eight years ago, seals a reconciliation between the two nations after a four-year rift ended in 2021.
"He [Sheikh Tamim] emphasised Qatar's resolve to bolster bilateral relations in all fields going forward through increasing Qatari investments in Egypt and taking advantage of available business opportunities there," Mr Radi said without giving details.
Sheikh Tamim's office, however, said Qatar and Egypt signed several agreements, including one between the Qatar Investment Authority and the Sovereign Fund of Egypt for investment and development.
Also signed were deals on "co-operation in the field of ports" and "co-operation in the field of social affairs", according to the official website of the emir's office.
It said Mr El Sisi and Sheikh Tamim discussed co-operation on investment, transport and social affairs.
The Egyptian leader's visit to Qatar comes at a time when Cairo is struggling to keep its economy afloat during a crisis mainly caused by the damaging fall-out from the Russia-Ukraine war and the coronavirus pandemic before it.
Egypt is currently negotiating with the IMF over structural economic reform and a possible loan from the Washington-based lender to shore up its economy, hit hard by a steeply higher import bill, slumping tourism revenues and a flight of foreign investments in its once-lucrative debt market.
Earlier on Wednesday, Mr El Sisi met Qatar's business leaders. Egypt was keen on expanding economic and business relations with Qatar, Mr El Sisi told the meeting, according to his spokesman.
Sheikh Tamim visited Egypt in June when his nation’s investments in the most populous Arab nation were high on the agenda of talks he held with Mr El Sisi.
Co-operation in the energy and agriculture sectors was also discussed.
In March, Cairo said Qatar planned to invest $5 billion in Egypt.
Seperatly on Wednesday, Egyptian authorities released Al Jazeera journalist Ahmed Al Nagdy from detention.
Meanwhile, QatarEnergy announced an agreement with US company ExxonMobil to acquire a 40 per cent stake in a gas exploration block off Egypt’s Mediterranean coast.
In June, Egypt's finance ministry said Qatar had made $3bn of deposits in Egypt's central bank three months earlier. It said that an additional $2bn to $3bn of investments were under discussion.
That was on top of deposits of $5bn from Saudi Arabia and $3bn from the UAE to Egypt's central bank in February and March this year, the ministry said.
The UAE and Saudi Arabia also made recent investments in Egypt through their sovereign wealth funds.
In 2017 Egypt, Saudi Arabia, the UAE and Bahrain severed diplomatic ties with Doha. This was over Qatar's support for the Muslim Brotherhood and its soft line on Iran.
The dispute was resolved and relations were restored in January last year.
Relations between Egypt and Qatar have traditionally been close, with their business ties surviving the recent rift nearly unscathed.
Qatar is home to tens of thousands of Egyptians who work there. They sent home $1.5 billion in the financial year 2020-2021, a 14.3 per cent increase over the previous year, according to Egypt’s state statistics bureau.
Qatar’s invested $507.9 million in Egypt in the financial year 2020-2021, the latest year for which figures are available.