On Saturday, he will be wearing the famous blue colours of Godolphin in the $10 million Dubai World Cup, the sport's richest race.
"It's amazing. I never thought I would be where I am today," the 32-year-old said. "It's great to be in a position like this."
De Sousa, signed earlier this year as understudy to Godolphin's top rider Frankie Dettori, said: "I am still learning every day. Frankie is for me one of the best jockeys in the world, so I have a lot to learn from him."
De Sousa narrowly lost out last season to Paul Hanagan in a prolonged duel for the jockeys' championship in Britain but he had caught the eye of the powerful Godolphin racing and breeding empire, brainchild of Sheikh Mohammed of Dubai.
An impressive debut on the competitive Dubai circuit early in 2012, boosted by a big-race double in February, led to an offer from Godolphin.
One of 10 siblings from Sao Paulo, things only really started for De Sousa when he moved from Ireland to the north of England five years ago. Since then the no-frills rider has attracted attention for his strength, allied to tactical acumen.
In Saturday's big race he partners Mendip for trainer Saeed bin Suroor with mentor Dettori on board Prince Bishop. Both are seen as 20-1 outsiders in London betting but De Sousa was positive.
"Mendip is a really smart horse and if puts his best effort into the race he could be thereabouts," he said. "I wish I could have had a better draw (stall 13 of 14) but it really doesn't matter to me. If he is right on the night the draw shouldn't be a problem."
Godolphin have two other runners in the shape of Capponi (12-1) and Monterosso (20-1) but ex-Australian champion So You Think, now trained by Aidan O'Brien in Ireland, is rated a firm 5-2 favourite.
Smart Falcon, 11-2 second favourite, seeks another win for Japan to follow the emotional success of Victoire Pisa in 2011.
Canada's versatile Chantal Sutherland will become the first woman to ride in the race when partnering third favourite Game On Dude (8-1) for U.S. trainer Bob Baffert.
Baffert, 59, suffered a heart attack earlier in the week but was released on Thursday and expects to be there on Saturday. He has won the race twice before, with Silver Charm (1998) and Captain Steve (2001).