Launch from Cape Canaveral (KSC); landing at Cape Canaveral (KSC), runway 15; ISS 15A ITS-S6.

The launch was scrubbed several times because of Shuttle problems in general with hydrogen flow control valves and then due to a leak in a liquid hydrogen vent line between the shuttle and the external tank. The result was the renounce of a planned fourth EVA during this mission, because the following Soyuz mission needed a docking port on the space station.

Following a two day solo flight Discovery docked to the ISS on March 17, 2009. Common work with the ISS expedition 18 was performed. Important was the transfer of Koichi Wakata to the ISS and Sandra Magnus to the STS-119 crew for returning to the Earth. The main goal of this mission was to deliver the S6 solar arrays to the ISS, completing the construction of the Integrated Truss Structure.

STS-119 also carried several experiments, including the Shuttle Ionospheric Modification with Pulsed Local EXhaust (SIMPLEX), Shuttle Exhaust Ion Turbulence Experiments (SEITE), and Maui Analysis of Upper Atmospheric Injections (MAUI). STS-119 was also used for the "Boundary Layer Transition Detailed Test Objective" experiment. One tile of the thermal protection system was raised 0.25 inches (6.4 mm) above the others so that, at about Mach 15 during reentry, a boundary layer transition would be initiated. This experiment was repeated during STS-128 with the tile raised to 0.35 inches (8.9 mm), tripping at Mach 18 to produce more heat.

The first EVA by Steven Swanson and Richard Arnold occured on March 19, 2009 (6h 07m). After Canadarm2 was released S6 and moved away, the spacewalkers plugged in power and data cables to connect the new hardware. The two spacewalkers also removed launch locks, stowed a keel pin, removed and jettisoned four thermal covers, and deployed the blanket boxes that hold the solar arrays in place during launch.

While extension of the new solar array wings originally was scheduled for Flight Day 8, the decision that no focused inspection of Discovery's heat shield was needed had freed up time in the flight plan to complete the deployment on Flight Day 6.

The second EVA was performed by Steven Swanson and Joseph Acaba on March 21, 2009 (6h 30m). First task during this spacewalk was to prepare a worksite for new batteries that will be brought up on the STS-127 mission. They loosened bolts, installed foot restraints. Steven Swanson installed a Global Positioning System antenna on the pressurized logistics module attached to the Kibo laboratory. They photographed areas of radiator panels extended from the Port 1 and Starboard 1 trusses and reconfigured connectors at a patch panel on the Zenith 1 truss that power Control Moment Gyroscopes. After struggling with a pin that kept an Unpressurized Cargo Carrier Attachment System (UCCAS) from fully deploying, they tied UCCAS safely in place.

Flight day 8 was mostly used for a free day, although work on the Urine Processor Assembly continued and they had to avoid a piece of orbital debris (from a former Chinese satellite).

The third and final EVA by Richard Arnold and Joseph Acaba was performed on March 23, 2009 (6h 27m) to move one of the station's two Crew and Equipment and Translation Aid - or CETA - carts. The carts were moved to the port side of the station's truss during the previous mission to give the robotic arm's mobile transporter the best possible access to the starboard truss for the installation of the new truss segment and solar arrays. With that work done, one of the carts was moved back to the station's port side, leaving a cart for use on either side of the truss. The CETA-cart also got a new coupler. The EVA also included lubricating the end effector capture snares on the station's robot arm - similar to what was done to the other end on an STS-126 spacewalk in late 2008. This has been proven to prevent the snare from snagging or not returning snugly into its groove inside the latching mechanism.

They were unable to deploy the Port 3 unpressurized cargo carrier attachment system (UCCAS). They secured the UCCAS in place until engineers can evaluate the problem. Mission Control cancelled the installation of a similar payload attachment system on the starboard side.

On Flight day 11 they had a press conference with President Obama, students and members of the Congress. They also handled final transfers from Discovery to the ISS.

Due of bad weather at Cape Canaveral (KSC) the landing was delayed for one orbit.

Koichi Wakata landed on July 31, 2009 at 14:48 UTC with STS-127.