With Sir John Fowler, he designed and engineered the Forth Bridge after the Tay bridge collapse.
It was a cantilever bridge and Baker gave numerous lectures on the principles which lay behind his design.
Thomas Bouch had originally been awarded the contract but he lost it after the Tay Bridge Inquiry reported in June 1880.
The bridge was built entirely in steel, much stronger than cast iron.
He used hollow steel tubes to create the cantilever, and it was then the largest bridge of its kind in the world.
The bridge is regarded as an engineering marvel.
It is 8,296 ft (2,529 m) in length, and the double track is elevated 151 feet (46 m) above high tide.
It consists of two main spans of 1,710 feet (520 m),  two side spans of 675 feet (206 m), 15 approach spans of 168 feet (51 m) and five of 25 feet (7.6 m) ).[3] Each main span comprises two 680 ft (210 m) cantilever arms supporting a central 350 ft (110 m) span girder bridge.
The three great four-tower cantilever structures are 340 ft (104 m) tall, each 70 ft (21 m) diameter foot resting on a separate foundation.
The southern group of foundations had to be constructed as caissons under compressed air, to a depth of 90 ft (27 m).
At its peak, approximately 4,600 workers were employed in its construction.
Initially, it was recorded that 57 lives were lost however after extensive research by local historians, the figure has been revised upwards to 98.
Eight men who fell from the bridge were saved by boats positioned in the river under work areas.
More than 55,000 tons of steel were used, as well as 18,122 m³ of granite and over eight million rivets.
The bridge was opened on 4 March 1890 by the Prince of Wales, later King Edward VII, who drove home the last rivet, which was gold plated and suitably inscribed.
A contemporary materials analysis of the bridge, c. 2002, found that the steel in the bridge is of good quality, with little variation.

The use of a cantilever in bridge design was not a new idea, but the scale of Baker's undertaking was a pioneering effort, later followed in different parts of the world.
Much of the work done was without precedent, including calculations for incidence of erection stresses, provisions made for reducing future maintenance costs, calculations for wind pressures made evident by the Tay Bridge disaster, the effect of temperature stresses on the structure, and so on.

Where possible, the bridge used natural features such as Inchgarvie, an island, the promontories on either side of the firth at this point, and also the high banks on either side.
The remains of Thomas Bouch's first attempts at his bridge can also be seen on the island.

The bridge has a speed limit of 50 mph (80 km/h) for passenger trains and 20 mph (32 km/h) for freight trains.
The weight limit for any train on the bridge is 1,422 tonnes (1,442,000 kg) although this is waived for the frequent coal trains, provided two such trains do not simultaneously occupy the bridge.
The route availability code is RA8, meaning any current UK locomotive can use the bridge, which was designed to accommodate heavier steam locomotives.
Up to 190–200 trains per day crossed the bridge in 2006.
A structure like the Forth Bridge needs constant maintenance and the ancillary works for the bridge included not only a maintenance workshop and yard but a railway "colony" of some fifty houses at Dalmeny Station.

"Painting the Forth Bridge" is a colloquial term for a never-ending task (a modern rendering of the myth of Sisyphus), coined on the erroneous belief that, at one time in the history of the bridge, repainting was required and commenced immediately upon completion of the previous repaint.
According to a 2004 New Civil Engineer report on contemporary maintenance, such a practice never existed, although under British Rail management, and before, the bridge had a permanent maintenance crew.

A contemporary repainting of the bridge commenced with a contract award in 2002, for a schedule of work expected to continue until March 2009, involving the application of 20,000 m² of paint at an estimated cost of £13
With Sir John Fowler, he designed and engineered the Forth Bridge after the Tay bridge collapse. It was a cantilever bridge and Baker gave numerous lectures on the principles which lay behind his design. Thomas Bouch had originally been awarded the contract but he lost it after the Tay Bridge Inquiry reported in June 1880. The bridge was built entirely in steel, much stronger than cast iron. He used hollow steel tubes to create the cantilever, and it was then the largest bridge of its kind in the world. The bridge is regarded as an engineering marvel. It is 8,296 ft (2,529 m) in length, and the double track is elevated 151 feet (46 m) above high tide. It consists of two main spans of 1,710 feet (520 m),  two side spans of 675 feet (206 m), 15 approach spans of 168 feet (51 m) and five of 25 feet (7.6 m) ).[3] Each main span comprises two 680 ft (210 m) cantilever arms supporting a central 350 ft (110 m) span girder bridge. The three great four-tower cantilever structures are 340 ft (104 m) tall, each 70 ft (21 m) diameter foot resting on a separate foundation. The southern group of foundations had to be constructed as caissons under compressed air, to a depth of 90 ft (27 m). At its peak, approximately 4,600 workers were employed in its construction. Initially, it was recorded that 57 lives were lost however after extensive research by local historians, the figure has been revised upwards to 98. Eight men who fell from the bridge were saved by boats positioned in the river under work areas. More than 55,000 tons of steel were used, as well as 18,122 m³ of granite and over eight million rivets. The bridge was opened on 4 March 1890 by the Prince of Wales, later King Edward VII, who drove home the last rivet, which was gold plated and suitably inscribed. A contemporary materials analysis of the bridge, c. 2002, found that the steel in the bridge is of good quality, with little variation.
The use of a cantilever in bridge design was not a new idea, but the scale of Baker's undertaking was a pioneering effort, later followed in different parts of the world. Much of the work done was without precedent, including calculations for incidence of erection stresses, provisions made for reducing future maintenance costs, calculations for wind pressures made evident by the Tay Bridge disaster, the effect of temperature stresses on the structure, and so on.
Where possible, the bridge used natural features such as Inchgarvie, an island, the promontories on either side of the firth at this point, and also the high banks on either side. The remains of Thomas Bouch's first attempts at his bridge can also be seen on the island.
The bridge has a speed limit of 50 mph (80 km/h) for passenger trains and 20 mph (32 km/h) for freight trains. The weight limit for any train on the bridge is 1,422 tonnes (1,442,000 kg) although this is waived for the frequent coal trains, provided two such trains do not simultaneously occupy the bridge. The route availability code is RA8, meaning any current UK locomotive can use the bridge, which was designed to accommodate heavier steam locomotives. Up to 190–200 trains per day crossed the bridge in 2006. A structure like the Forth Bridge needs constant maintenance and the ancillary works for the bridge included not only a maintenance workshop and yard but a railway "colony" of some fifty houses at Dalmeny Station.
"Painting the Forth Bridge" is a colloquial term for a never-ending task (a modern rendering of the myth of Sisyphus), coined on the erroneous belief that, at one time in the history of the bridge, repainting was required and commenced immediately upon completion of the previous repaint. According to a 2004 New Civil Engineer report on contemporary maintenance, such a practice never existed, although under British Rail management, and before, the bridge had a permanent maintenance crew.
A contemporary repainting of the bridge commenced with a contract award in 2002, for a schedule of work expected to continue until March 2009, involving the application of 20,000 m² of paint at an estimated cost of £13
Benjamin Baker (engineer)