Timothy Grant Southee or Tim Southee began his cricketing journey by participating in under-19 cricket for New Zealand from 2006 to 2009. During this period, he played 13 one-day matches, including 10 in ICC Under-19 World Cups, and a drawn three-match Youth Test series against India in early 2007.

Southee's under-19 career culminated at the 2008 ICC Under-19 Cricket World Cup, where he was recognized as the player of the tournament. Southee made his under-19 debut at the age of 17 in the 2006 ICC Under-19 World Cup against Bangladesh in Colombo, Sri Lanka. He also played against Pakistan, Ireland, the United States, and Nepal in that tournament.

In 2007, when New Zealand hosted India, Southee displayed his talent in his only three Youth Tests. In the second match of the series, he claimed figures of 6–36 and 6–56 in a victory for New Zealand, finishing the series with 20 wickets at an average of 18.2.

By the time Southee participated in his second ICC Under-19 World Cup in Malaysia in 2008, he had already played two full Twenty20 internationals for New Zealand. His exceptional bowling performance in the tournament earned him the player of the tournament award. He took 5/11 against Zimbabwe and claimed a total of 17 wickets in five matches, with an average of only 6.64 and an economy rate of 2.52 runs per over. Southee's final under-19 appearance was in New Zealand's semi-final loss to eventual champions India.

Following his last under-19 appearance, Southee swiftly entered test cricket. Among his peers were future international players like Kane Williamson, Martin Guptill, Trent Boult, Corey Anderson, Hamish Rutherford, and Hamish Bennett. Southee debuted across formats: Twenty20, one-day internationals, and test matches. National bowling coach Dayle Hadlee recognized his potential, likening his skill to Glenn McGrath during a 2007 visit to India. This led to Southee's inclusion in discussions for the upcoming England tour.

Southee continued to impress, taking 6/68 in a first-class match against Auckland on his 19th birthday in early December. He was then selected to play for a New Zealand XI in a charity Twenty20 match against Bangladesh on December 23, 2007, where he took 1/31.

Southee's official entry into international Twenty20 cricket came when he was named in the New Zealand squad for two Twenty20 International games against England on January 30, 2008. He made his debut on February 5, 2008, in Auckland, taking 1/38. In the second match, he emerged as New Zealand's top bowler with figures of 2/22 from four overs.

Despite his promising start in the international arena, Southee briefly rejoined the national Under-19 team for the 2008 Under-19 Cricket World Cup in Malaysia.

After being named the player of the tournament at the 2008 Under-19 World Cup, Southee quickly transitioned into the senior ranks of New Zealand cricket.

Southee debuted in Test cricket against England in March 2008 at 19 years and 102 days, impressing with figures of 5/55 and scoring an unbeaten 77 runs off 40 balls in the second innings, setting a record for New Zealand's fastest half-century.

In the 2009–2010 season, Southee established himself as a regular in the New Zealand team, featuring in 18 international matches against Pakistan, Bangladesh, and Australia.

During Pakistan's tour of New Zealand in the 2010–11 season, Southee shone with a hat-trick in international Twenty20 cricket and his first ODI five-wicket haul, earning him the T20 Player of the Year award from NZC.

In the 2011 ICC Cricket World Cup, Southee emerged as the third-highest wicket-taker with 18 wickets, earning recognition in the ICC's "team of the tournament" as the 12th man.

Southee's stellar form continued beyond the World Cup, leading to his inclusion in the Chennai Super Kings squad for the IPL's 2011 season and his record-breaking performance of 6/16, including a hat-trick, for English county Essex in the 2011 Friends Life t20. In subsequent seasons, Southee's consistency and impact remained evident, with standout performances against India, the West Indies, and his selection in the ICC World Test XI in 2014.

The 2015 Cricket World Cup showcased Southee's brilliance once again, as he delivered his career-best bowling figures of 7/33 against England, playing a crucial role in New Zealand's victory.

In May 2018, Southee was among the twenty players granted new contracts for the 2018–19 season by New Zealand Cricket. Subsequently, on 3 June 2018, he was drafted into the Vancouver Knights for the inaugural Global T20 Canada tournament.

In August 2019, during the series against Sri Lanka, Southee became the fourth New Zealand bowler to secure 250 wickets in Test cricket. He also equaled Sachin Tendulkar's record of 69 sixes in Test cricket during the same month.

In November 2022, during India's tour of New Zealand, Southee secured his second hat-trick in T20Is, joining Sri Lankan bowling legend Lasith Malinga in the exclusive group of T20I bowlers with multiple hat-tricks.

Later, on 29 December 2020, Southee became the third New Zealand bowler to achieve 300 wickets in Test cricket during the First Test of the series against Pakistan.

In December 2022, Tim Southee assumed the role of full-time Test captain for the Blackcaps following Kane Williamson's resignation from the position. In his inaugural series as captain, New Zealand achieved a 0-0 draw against Pakistan. Subsequently, in their first Test series at home under Southee's leadership, the Blackcaps shared the honors with England in a two-Test series.

Notably, on February 28, 2023, New Zealand clinched a thrilling victory against England by a single run after being asked to follow-on earlier in the match. This historic win made them only the second team, following the West Indies, to secure a Test victory by such a narrow margin and the fourth team overall to triumph after being asked to follow-on.

In February 2023, Tim Southee etched his name in history by becoming the first player from New Zealand to achieve 700 international wickets. He reached this remarkable milestone during the 2nd Test of England's tour of New Zealand, 2023, when he dismissed Ben Duckett.

Tim Southee, absent from IPL 2024, is utilizing the off-season to strategize for the three-match Test series against India in October.