Stevenson, who is 28, has played 39 times for Ulster. His excellent form for the province this season saw him included in the extended Ireland training squad for the RBS 6 Nations. He made his O2 Ireland Wolfhounds debut against England Saxons last month.
The 29-year-old McComb has represented Ulster on 29 occasions. He signed his first senior contract for the 2010/11 season and made his first Heineken Cup start in the away win over Castres Olympique last month.
Doyle, who is 23, arrived at Ulster at the start of this season. He made a promising start to his career at Ravenhill, but a broken leg, sustained during his debut appearance for Dungannon, has meant that it has been a frustrating six months for the Australian-born openside flanker.
Commenting on the contract extensions, Ulster director of rugby David Humphreys said: "I am delighted that these three players have committed to Ulster in the long-term.
"Lewis and Neil have been important to us all season, while Sean showed in his first few games what an exciting prospect he is. I have no doubt that they will only get better as players and that is good for Ulster Rugby."