In round 1 of the season, Guerra made his NRL debut for the Sydney Roosters, against the South Sydney Rabbitohs at ANZ Stadium, scoring a try off the interchange bench in the Roosters 36-10 win. Guerra played for New South Wales residents against the Queensland residents team, scoring a try in the 28-20 win. Guerra finished his debut year with 3 tries from 9 matches.
Guerra played in 14 matches and scored 6 tries for the Roosters in 2011. He was announced as a member of the Italian side that competed in 2013 World Cup qualifying, but again did not feature.
2012
Guerra played in 19 matches and scored 5 tries for the Roosters in the 2012 NRL season.
2013
In the 2013 NRL Grand Final, Guerra played at second-row and scored a try in the Roosters 26-18 victory over the Manly-Warringah Sea Eagles. Guerra played in 22 matches and scored 6 tries in the Roosters successful 2013 NRL season. In the post season, Guerra made his international debut playing for Italy in the 2013 World Cup. He played all 3 matches at centre and scored 2 tries against Wales in Italy’s 32-16 win at Millennium Stadium.
2014
In May, Guerra was named as the only change to the Queensland team for game 1 of the 2014 State of Origin series in place of the injured Sam Thaiday. He made his debut in the Maroons 8-12 loss at Suncorp Stadium. Guerra started at second-row in game 2, as the Maroons lost again, 4-6. In game 3, at Suncorp Stadium, Guerra scored his first origin try in the Maroons 32-8 win. Guerra finished off the Roosters season with 23 matches from 6 tries. On 14 October, Guerra was selected in the Australian Kangaroos 24-man squad for the 2014 Four Nations. He made his Australian debut and played his only match in the tournament in the 30-12 loss against New Zealand off the interchange bench at Suncorp Stadium. On 23 December, Guerra extended his contract with the Roosters to the end of the 2017 season.
2015
Guerra retained his State of Origin spot in the second-row for all 3 matches in 2015, scoring a try in the 3rd match. In round 20, against the Wests Tigers, he played his 100th NRL career match in the 33-8 win at the Sydney Football Stadium. Guerra scored 5 tries from his 22 NRL matches.
2016
Despite playing in all 3 State of Origin matches, Guerra was moved to the bench by the Roosters, and then dropped to reserve grade later in the season. He said, "Getting dropped always hurts whether you know you deserve it or not. But I felt that I deserved to be dropped and it was up to me if I got that reprieve to make the most of it and show I deserved to be out there. It has been hard. I have been trying to put my finger on it for 24 rounds. Some games have been good, but too many haven't." Guerra finished the season with 21 matches and 4 tries for the Roosters.
2017
Guerra played off the bench in the first State of Origin game of the series. After the shock defeat, Guerra was one of many players to be axed from the Maroons squad for fresher blood for Game 2. On 15 June, it was announced that Guerra signed a 3-year contract with the Newcastle Knights starting in 2018. In Round 23 against the Melbourne Storm, Guerra played his 150th NRL match in the 16-13 loss at AAMI Park. Guerra finished his last year with the Sydney Roosters with 24 matches and 5 tries. At the end of the season, he was named in the training squad for Italy for the 2017 Rugby League World Cup but later ruled himself out.
