[12] In 2003, Gil joined the Clube Escola Ténis de Oeiras, led by his mentor and future coach, whom he would later abandon João Cunha e Silva.

[11] While growing up, his idol was Andre Agassi and his favorite hobbies include computers, video games, internet, gadgets and golf.

Gil made his debut in a junior tournament in July 2000 at the Grade 4 Taça Diogo Nápoles in Porto, by playing the main draw in the doubles event.

[18] At the 2004 Estoril Open, Gil made his ATP Tour debut playing the doubles event alongside Bernardo Mota and reached the quarterfinals.

[22] Gil began 2005 season with two straight singles titles and one doubles runner-up at Futures tournaments in Faro and Lagos between February and March.

[23][24] At ATP Tour level, Gil entered again in the Estoril Open doubles event and lost in the first round with Leonardo Tavares.

[22] Gil made his first attempt to enter the main draw of a Grand Slam tournament at the 2007 French Open, but lost in the final match of the qualifying rounds.

He won one singles titles in Seville in September, and reached four doubles finals (Bogotá, Karlsruhe, Fürth and Manerbio).

[34] The next month, Gil was called up for the Portugal Davis Cup team to face Tunisia and won his singles match against Malek Jaziri.

[35] Then, he entered his first ATP Tour of the season at the Estoril Open where he reached the quarterfinals for the second time, after wins over Nicolas Mahut and João Sousa.

[2] After skipping the Australian Open, Gil began his 2009 season with back-to-back semifinals appearances in ATP World Tour tournaments.

[41][42] At the SA Tennis Open, he defeated Guillermo García López to become the second Portuguese to reach the semifinals at this level, after his coach João Cunha e Silva in 1992.

[41][44] In result, he broke his shared record with Nuno Marques and became the sole holder of the highest ranking ever for a Portuguese player, at no.

[48] Gil continued his form with a quarterfinals presence at the Grand Prix Hassan II, and fell in the second round at the Barcelona Open to Nadal again.

[41] In May, Gil was the first Portuguese to enter the main draw of the Estoril Open thanks to his world ranking, but was eliminated in the first round by James Blake.

Facing Algeria, he won his singles and doubles matches, thus helping Portugal to secure a place in the Europe/Africa Zone Group II the following year.

[53] After losing in the first round of another ATP tournament, the Romanian Open, Gil decided to move back to the Challenger Tour – he won singles and doubles title in Napoli in the end of September.

[56] Making his main draw debut at the Australian Open, Gil retired during a first round match against David Ferrer, when was trailing 6–0, 6–0, 2–0.

[63] However, he partnered Daniel Gimeno Traver in the doubles event to reach the third round of a Grand Slam tournament for the first time, where they lost to fifth seeds Łukasz Kubot and Oliver Marach.

[64] Gil's three wins over Bosnia and Herzegovina at the Davis Cup in September contributed for Portugal's promotion to Europe/Africa Zone Group I in 2011.

[22][25] After participating in Challenger tournaments, Gil returned to the ATP Tour in October, losing in the second round at the Open Sud de France.

[56][57] In the year's last ranking, Gil was positioned 101 in the world – thus failing to keep his top 100 status from the previous season and behind his fellow countryman Machado.

[65] Then, he won his first match at a Grand Slam tournament and became the first Portuguese since Nuno Marques in 1991 to do so at the Australian Open, with a 5-set win over Pablo Cuevas.

Gil was initially invited for the Estoril Open as a wildcard, in virtue of his low ranking, but he eventually qualified directly, because of pre-tournament drop-outs.

In November, he reached the quarter-finals in the Buenos Aires Challenger in his last tournament of the season losing to his friend Gastão Elias by 1–6, 7–5, 7–5 in 2h57m after his opponent saved 2 match points when Gil was leading by 6–1, 5–4.

Gil then made history by becoming the first Portuguese tennis player to reach the 3rd round of a Grand Slam tournament after downing Spain's Marcel Granollers (28th) in 4 sets by 6–3, 4–6, 6–4, 6–3, in 2h48m.

In May, he won in doubles a future in Coimbra with Gonçalo Falcão, in what turned out to be his last match before a temporary retirement from professional tennis.

During the 2006 Estoril Open, Dmitry Tursunov made death threats to Gil for taking too much time in-between points.

Richard Gasquet accused him of screaming too loud in 2007, and Nicolás Almagro attempted to hit Gil with a ball after similar complaints during a 2009 Brasil Open match.

[12] Gil signed a sponsorship deal with sportswear and equipments producer Asics in 2009, which combined monetary and material support.