The Phase III trial of the two-dose vaccination will be carried out in nine hospitals throughout Spain on volunteers both with and without previous health conditions, the AEMPS agency said in a statement.
J&J started mid-stage phase II trials in Spain and other countries in September and launched a late-stage trial in Britain on Monday.
The Phase III trials will be carried out on 30,000 volunteers in nine countries.
The two-dose study will run in parallel with a trials of a single shot regimen involving 60,000 participants which was launched in September.
The Spanish hospitals involved in the trials will enrol volunteers as soon as possible, the AEMPS said, adding that 20% will be younger than 40 and 30% older than 60.
They will be given a first dose of either a placebo or the experimental shot, currently called Ad26COV2, followed by a second dose or placebo later.
Conclusions will only be available after analysing the data at the end of the trials, the Spanish medicines agency said.