Nitsch worked part-time as a pilot for Tyrolean Airways.
Nitsch holds the No-Limits record, the title of "Deepest man on Earth" in which the diver can make use of a weighted sled to descend as far as possible and uses an air-filled balloon to return to the surface. Nitsch set the world record in Spetses, Greece in June 2007 when he descended to 214 m (702 ft), beating his own record of 183 m (600 ft) set the previous year. He also held the world record in the Constant Weight event, which is considered by many to be the classic free-diving discipline: the diver descends next to a line, not using the line and unaided by a sled, and must maintain a constant weight, meaning that no weight can be dropped for the return to the surface. Nitsch exceeded the then world record in 2006 when he dived to a depth of 110 m (361 ft), but failure to complete the strict surfacing protocols within the allotted time meant that the dive was disqualified. In Hurghada, Egypt, in December 2006 he did a Constant Weight World Record dive of 111 m (364 ft), adding 2 m on top of Guillaume Néry's previous record.
Later in 2007, he also set the Constant weight (No Fins) record during The Triple Depth in Dahab, Egypt, and went on to push the Constant record to 112 m (367 ft) during the World Championships in Sharm. Herbert also won the AIDA Individual World Championships.
Of the other five AIDA recognised events, Nitsch has been the world record holder in four: Static Apnea, Dynamic Apnea, Free Immersion and Dynamic apnea without fins. He set a time of 9 mins 4 secs for the world Static Apnea record in December 2006 when he held his breath underwater in a swimming pool in Hurgada, a time that was beaten by 4 secs in 2007 by Tom Sietas of Germany. His record of 66 m (217 ft) for Constant Weight without fins, set in 2004, was beaten by 14 m in 2005 by Czech free-diver, Martin Štěpánek, who is also the holder of the Free Immersion record of 106 m (348 ft); Nitsch recorded 100 m (328 ft) in September 2003, but his record was bettered by a dive of 101 m by Carlos Coste of Venezuela in October the same year and then twice improved upon by Štěpánek. Nitsch's Dynamic Apnea record, 183 m set in 2002, has been beaten by 40 m by Tom Sietas and women's champion, Natalia Molchanova of Russia, has also swum further than 200 m. Sietas also holds the Dynamic apnea without fins record at 183 m, beating Nitsch's 2001 distance of 134 m by almost 50 m.
During the 2009 Vertical Blue competition at the Dean's Blue Hole in Bahamas, he broke the Free Immersion world record at 109 m (358 ft). On the last day of the competition, he performed a world record dive in Constant Weight at 120 m (394 ft), beating by 6 m the previous record that he had set a few days earlier. He used his arms only in the last 40 m (131 ft) of this ascent, with a total dive time of 3:58.
In 2012, Nitsch returned to the "No Limits" category in the waters off Santorini, Greece, with a project labeled "Extreme 800", aiming for a depth of 244 meters, the round number of 800 feet. An original intention of having also this dive sanctioned by AIDA fell through due to a sponsoring conflict between the two watchmakers Breitling (supporting Nitsch and the record project) and Suunto (supporting AIDA), leaving no officiating body to homologue the dive.
Following extensive training using an innovative torpedo-type sled design of very high descend and ascend speed, on June 6 Nitsch managed to reach a depth of 253.2 meters (831 ft), but during the last ten meters of the ascend he was reported to require assistance by safety freedivers, while experiencing serious symptoms of decompression sickness. Later, Nitsch declared on his blog that at the target depth, he suffered what he himself called a bewildering "blackout through narcosis" (as opposed to through oxygen starvation), and then waking up during the ascend. Following a planned post-dive decompression, breathing medical oxygen at a shallow depth, he told his support team that he felt much weaker than normal, and his condition was assessed as critical enough to require an air transfer to a pre-alerted decompression chamber in Athens, where he received treatments. Nitsch subsequently received extensive decompression treatment in Germany.
72m = AIDA Lake Record; after 2001-12-31 AIDA International no longer separated the records achieved in a lake from those in the sea.