Singh tweeted that the Wednesday morning meeting was "excellent" and "we reviewed the full range of India-US defence cooperation".
External Affairs Minister S. Jaishankar was scheduled to also have a bilateral meeting on Wednesday with US Secretary of State Mike Pompeo before the joint meeting of the four leaders.
Pompeo tweeted before the meeting: "Throughout 2019 we've seen rapid growth in the #USIndia strategic partnership."
He said he was pleased to host Jaishankar and Singh for the 2+2 Dialogue "as we aim to review our successes and take this vital relationship to the next level".
Wednesday's 2+2 comes at a time of close cooperation between the two countries in defence with a focus on the Indo-Pacific region and US backing on the diplomatic front, even though there has been a setback in trade.
This is the second edition of the 2+2 Dialogue marking the close ties between the world's largest and most powerful democracies.
Then Defence Minister Nirmala Sitharaman and then External Affairs Minister Sushma Swaraj hosted Pompeo and then Defence Secretary Jim Mattis for the inaugural 2+2 last year in New Delhi.
Ahead of the 2+2 Dialogue, Rajnath Singh visited the Norfolk naval base on Tuesday where he watched a static display and flight demonstration by Boeing Super Hornet F/A-18E multi-action jets and boarded the Nimitz-class aircraft carrier USS Dwight D. Eisenhower.
(Arul Louis can be contacted at arul.l@.in and followed on Twitter @arulouis)
( With inputs from IANS )