The 23-year-old had his medical over the weekend and signed the contract, but had to return to London to finish the paperwork for a visa and work permit.
According to Sky Sport Italia, the details of the complicated agreement have been released and show how the Giallorossi were able to afford it.
The total cost of the operation will be €40m plus performance-related bonuses.
Chelsea will only receive €5m of it this summer, another €20m by the summer of 2024 in various instalments and a further €15m for the 2024-25 campaign.
The Premier League side can also retain a buy-back option on Abraham worth €80m, but it is only valid from July 2023.
The England international’s salary is expected to be worth €4.5m net, but that is thanks to the Italian tax credit aimed to bring foreign talent into the country, so it is ‘only’ €5.8m gross for Roma.
— Gianluca Di Marzio (@DiMarzio) August 16, 2021