2001

Nicholas competed in doubles in his first main-draw Futures match. He and partner (compatriot) Tripp Phillips lost in the first round of USA F21. This was the only tour event he competed in 2001.^[1]

2002

Monroe reached the quarterfinals of his first Futures tournament in singles play, USA F11, played in Peoria, Illinois in July.

2003

Nicholas won his first Futures doubles match, partnering Yannis Vlachos to the semifinals of Slovenia F1.^[1]

2004: Turned Pro

After playing only four Futures events in 2003, Monroe played, from June, a full schedule in 2004. In his first doubles tournament of the year, he reached his first final, partnering Jonathan Igbinovia. In August he reached his first singles semifinal, at Indonesia F2 in Makassar. In October, Monroe captured his first doubles Futures title, in doubles, partnering Márcio Torres, at Venezuela F3. He won a second two weeks later, Mexico F17, playing alongside Jeremy Wurtzman. Later in November, Monroe played in his first Challenger tournament, the Puebla Challenger in Puebla, Mexico, losing in the first round to Santiago González. In doubles, he and Wurtzman reached the semifinals. Three weeks later in Guadalajara, however, he won two Challenger matches to reach the quarterfinals.

2005

His first full year as a professional, Nicholas played ITF Circuit and USTA Pro Circuit events. He reached his first final and won his first singles title at the ITF Circuit event in South Africa, when he defeated Stephen Mitchell. Highly successful in doubles, Nick won four titles in 2005: with Jeremy Wurtzman at the USTA Pro Circuit event in Orange Park, Florida; with Izak van der Merwe at ITF Circuit events in Botswana and Zimbabwe; and with Sam Warburg at the ITF Circuit event in Israel.

Monroe competed in 29 events in 2005, all but one of which were Futures. He lost in the first round of his only main draw Challenger event singles match, to Zack Fleishman at the Cuenca Challenger. Monroe won his first singles title, South Africa F1 in late October, defeating Stephen Mitchell in the final.^[1]

2006

Nicholas started the year by winning the ITF Circuit title in Costa Rica. A month later, he won another ITF title, this time in Nigeria. He reached the semifinals of a USTA Pro Circuit event in Little Rock, before reaching back-to-back finals in India. He lost to Karan Rastogi in Delhi and defeated Sunil-Kumar Sipaeya in Dehradun. He reached another ITF Circuit final in the fall in Japan, where he lost to Satoshi Iwabuchi. At the beginning of the year, Nick won consecutive doubles titles on the ITF Circuit with partner Sam Warburg in Mexico and Costa Rica.^[1]

2007

Nicholas began the year by attempting to qualify for the 2007 Australian Open. He defeated Jeremy Chardy in his first round singles qualifying match. He reached consecutive ITF Futures events in Japan, where he lost to Gouichi Motomura both times. He won two titles at ITF Futures events in Mexico and won a USTA Pro Circuit event in Rochester, New York, where he defeated Robert Yim in the final. The fall of 2007 saw Monroe reach the semifinals of USTAPro Circuit events in Manchester, Texas, where he lost to eventual champion Michael McClune, and Waikoloa, Hawaii where he lost to Lester Cook. He partnered with Izak van der Merwe to win the USTA Pro Circuit doubles title in Brownsville, Texas.^[1]

2012: Challenger circuit doubles success

Nicholas won the Challenger in Medellin, Colombia (doubles) with his partner Maciek Sykut.

He also won two doubles Challengers in Mexico with German partner, Simon Stadler. ^[4]

2013–2015: First Three ATP doubles titles

Monroe at the 2013 Wimbledon Championships

Nicholas had his best year as a professional in 2013, finishing the year with a doubles Ranking of World No. 53. In January 2013, Monroe and partner Raven Klaasen made it to the semifinals of the 2013 Aircel Chennai Open, falling to Benoît Paire and Stanislas Wawrinka, after a surprise quarterfinal win over the #1 Seeds Mahesh Bhupathi and Daniel Nestor. He then teamed up successfully with Simon Stadler to play the Copa Claro in Buenos Aires, Argentina. They made it to the final, falling to the Italian pair of Fabio Fognini and Simone Bolelli. In July 2013, he won his first ATP title in doubles also with Stadler at the 250 level at the 2013 Bastad Skistar Swedish Open and reached the final of the 2013 Umag Open in Croatia also on clay.

2017–18: Continued doubles success: First Masters final & US Open quarterfinal, top 30 debut

Following three semi-final finishes in Chennai, Auckland and Quito all with Artem Sitak, Monroe reached a top 40 doubles ranking of No. 39 on 3 April 2017 after the biggest run of his career to the final of the 2017 Miami Open with Jack Sock.^[5] He later peaked at a career-high of No. 30 on 2 October 2017 after reaching his ninth final at the 2017 ATP Shenzhen Open partnering Nikola Mektic.

Partnering Artem Sitak he reached the third round at the 2017 Wimbledon Championships for their first time at this Major and in his career. With John-Patrick Smith at the 2017 US Open (tennis), he reached the quarterfinals at a Grand Slam also for the first time in his career.

The pair also won the title at the 2018 Atlanta Open, and reached earlier in February 2018 the final at the 2018 Delray Beach Open, Monroe’s tenth.

2019–2021: Thirteenth final, Second Major quarterfinal at the French Open

Monroe reached the final of the 2019 Winston-Salem Open partnering compatriot Tennys Sandgren.

Partnering fellow American Tommy Paul, he also reached at the 2020 French Open the second doubles Grand Slam quarterfinal of his career.

He reached the third round at the 2021 Australian Open for the first time at this Major partnering compatriot Frances Tiafoe.

2022: Retirement

He entered the main draw at the 2022 Wimbledon Championships as an alternate pair again with Tommy Paul.^[6] He played his last match on the ATP tour at the 2022 US Open (tennis) with Keegan Smith (tennis) ad a wildcard pair, where they lost to Fabio Fognini and Simone Bolelli in the second round.

ATP Masters 1000 finals

Doubles: 1 (1 runner-up)

Result	Year	Tournament	Surface	Partner	Opponents	Score
Loss	2017	Miami Open	Hard	Jack Sock	Łukasz Kubot Marcelo Melo	5–7, 3–6

Doubles: 13 (4 titles, 9 runner-ups)

Result	W–L	Date	Tournament	Tier	Surface	Partner	Opponents	Score
Loss	0–1	Feb 2013	Argentina Open, Argentina	250 Series	Clay	Simon Stadler	Simone Bolelli Fabio Fognini	3–6, 2–6
Win	1–1	Jul 2013	Swedish Open, Sweden	250 Series	Clay	Simon Stadler	Carlos Berlocq Albert Ramos Viñolas	6–2, 3–6, [10–3]
Loss	1–2	Jul 2013	Croatia Open, Croatia	250 Series	Clay	Simon Stadler	Martin Kližan David Marrero	1–6, 7–5, [7–10]
Win	2–2	Jul 2014	Swedish Open, Sweden (2)	250 Series	Clay	Johan Brunström	Jérémy Chardy Oliver Marach	4–6, 7–6(7–5), [10–7]
Loss	2–3	Apr 2015	Romanian Open, Romania	250 Series	Clay	Artem Sitak	Marius Copil Adrian Ungur	6–3, 5–7, [15–17]
Loss	2–4	Jul 2015	Hall of Fame Open, United States	250 Series	Grass	Mate Pavić	Jonathan Marray Aisam-ul-Haq Qureshi	6–4, 3–6, [8–10]
Win	3–4	Oct 2015	Stockholm Open, Sweden	250 Series	Hard (i)	Jack Sock	Mate Pavić Michael Venus	7–5, 6–2
Loss	3–5	Apr 2017	Miami Open, United States	Masters 1000	Hard	Jack Sock	Łukasz Kubot Marcelo Melo	5–7, 3–6
Loss	3–6	Oct 2017	Shenzhen Open, China	250 Series	Hard	Nikola Mektić	Alexander Peya Rajeev Ram	3–6, 2–6
Loss	3–7	Feb 2018	Delray Beach Open, United States	250 Series	Hard	John-Patrick Smith	Jack Sock Jackson Withrow	6–4, 4–6, [8–10]
Loss	3–8	May 2018	Istanbul Open, Turkey	250 Series	Clay	Ben McLachlan	Dominic Inglot Robert Lindstedt	6–3, 3–6, [8–10]
Win	4–8	Jul 2018	Atlanta Open, United States	250 Series	Hard	John-Patrick Smith	Ryan Harrison Rajeev Ram	3–6, 7–6(7–5), [10–8]
Loss	4–9	Aug 2019	Winston-Salem Open, United States	250 Series	Hard	Tennys Sandgren	Łukasz Kubot Marcelo Melo	7–6(8–6), 1–6, [3–10]

Doubles: 33 (13–20)

Result	W–L	Date	Tournament	Surface	Partner	Opponents	Score
Loss	0–1	Feb 2005	Joplin, United States	Hard (i)	Jeremy Wurtzman	Rik de Voest Łukasz Kubot	6–7(4–7), 4–6
Loss	0–2	Jun 2006	Yuba City, United States	Hard	Horia Tecău	Scott Lipsky David Martin	0–6, 4–6
Loss	0–3	Aug 2006	Manta, Ecuador	Hard	Horia Tecău	Eric Nunez Jean-Julien Rojer	3–6, 2–6
Loss	0–4	Jul 2007	Winnetka, United States	Hard	Izak van der Merwe	Patrick Briaud Chris Drake	6–7(5–7), 4–6
Loss	0–5	Sep 2007	Donetsk, Ukraine	Hard	Patrick Briaud	Philipp Petzschner Simon Stadler	5–7, 6–3, [6–10]
Win	1–5	Jun 2008	Yuba City, United States	Hard	Michael Yani	Jan-Michael Gambill Scott Oudsema	6–4, 6–4
Loss	1–6	Jul 2008	Granby, Canada	Hard	Alberto Francis	Philip Bester Peter Polansky	6–2, 1–6, [5–10]
Loss	1–7	Sep 2008	Waco, United States	Hard	Alberto Francis	Alex Bogomolov Jr. Dušan Vemić	4–6, 7–5, [8–10]
Win	2–7	Nov 2008	Puebla, Mexico	Hard	Eric Nunez	Daniel Garza Santiago González	4–6, 6–3, [10–6]
Win	3–7	May 2010	Carson, United States	Hard	Brian Battistone	Artem Sitak Leonardo Tavares	5–7, 6–3, [10–4]
Loss	3–8	Oct 2010	Sacramento, United States	Hard	Donald Young	Rik de Voest Izak van der Merwe	6–4, 4–6, [7–10]
Loss	3–9	Sep 2011	Bangkok, Thailand	Hard	Ludovic Walter	Pierre-Ludovic Duclos Riccardo Ghedin	4–6, 4–6
Loss	3–10	Oct 2011	Sacramento, United States	Hard	Jack Sock	Carsten Ball Chris Guccione	6–7(3–7), 6–1, [5–10]
Loss	3–11	Jan 2012	Honolulu, United States	Hard	Jack Sock	Amer Delić Travis Rettenmaier	4–6, 6–7(3–7)
Loss	3–12	Feb 2012	Dallas, United States	Hard (i)	Jack Sock	Chris Eaton Dominic Inglot	7–6(8–6), 4–6, [17–19]
Win	4–12	Apr 2012	Barranquilla, Colombia	Clay	Maciek Sykut	Marcel Felder Frank Moser	2–6, 6–3, [10–5]
Win	5–12	Apr 2012	San Luis Potosí, Mexico	Clay	Simon Stadler	Andre Begemann Jordan Kerr	3–6, 7–5, [10–7]
Loss	5–13	May 2012	Tunis, Tunisia	Clay	Simon Stadler	Jerzy Janowicz Jürgen Zopp	6–7(1–7), 3–6
Win	6–13	Jul 2012	Milan, Italy	Clay	Simon Stadler	Andrey Golubev Yuri Schukin	6–4, 3–6, [11–9]
Loss	6–14	Oct 2012	Belém, Brazil	Hard	Simon Stadler	John Peers John-Patrick Smith	3–6, 2–6
Loss	6–15	Oct 2012	San Juan, Argentina	Hard	Simon Stadler	Martín Alund Horacio Zeballos	6–3, 2–6, [12–14]
Win	7–15	Nov 2012	Medellín, Colombia	Clay	Simon Stadler	Renzo Olivo Marco Trungelliti	6–4, 6–4
Loss	7–16	May 2013	Bordeaux, France	Clay	Simon Stadler	Christopher Kas Oliver Marach	6–2, 4–6, [1–10]
Win	8–16	Jun 2013	Prostějov, Czech Republic	Clay	Simon Stadler	Mateusz Kowalczyk Lukáš Rosol	6–4, 6–4
Win	9–16	Aug 2013	San Marino, San Marino	Clay	Simon Stadler	Daniele Bracciali Florin Mergea	6–2, 6–4
Loss	9–17	Oct 2013	Rennes, France	Hard (i)	Simon Stadler	Oliver Marach Florin Mergea	4–6, 6–3, [7–10]
Win	10–17	Nov 2014	Geneva, Switzerland	Hard (i)	Johan Brunström	Oliver Marach Philipp Oswald	5–7, 7–5, [10–6]
Loss	10–18	May 2015	Aix-en-Provence, France	Clay	Artem Sitak	Robin Haase Aisam-ul-Haq Qureshi	1–6, 2–6
Win	11–18	Jul 2015	Winnetka, United States	Hard	Johan Brunström	Sekou Bangoura Frank Dancevic	4–6, 6–3, [10–8]
Loss	11–19	Sep 2015	Cary, United States	Hard	Austin Krajicek	Chase Buchanan Blaž Rola	4–6, 7–6(7–5), [4–10]
Loss	11–20	Nov 2015	Champaign, United States	Hard (i)	Austin Krajicek	David O'Hare Joe Salisbury	1–6, 4–6
Win	12–20	Mar 2016	Irving, United States	Hard	Aisam-ul-Haq Qureshi	Chris Guccione André Sá	6–2, 5–7, [10–4]
Win	13–20	Nov 2018	Houston, United States	Hard	Austin Krajicek	Marcelo Arévalo James Cerretani	4–6, 7–6(7–3), [10–5]